Grammage Explained

Grammage and basis weight, in the pulp and paper industry, are measures of the area density of a paper product, that is, its mass per unit of area. Two common ways of expressing the area density of a paper product are used:

Grammage

In the metric system, the mass per unit area of all types of paper and paperboard is expressed in terms of grams per square metre (g/m2). This quantity is commonly called grammage in both English and French,[2] though printers in most English-speaking countries still refer to the "weight" of paper.

Grammage=

mass(g)
length(m) x width(m)

Typical office paper has 80g/m2, therefore a typical A4 sheet (of a square metre) weighs 5g. The abbreviation gsm instead of the standard g/m2 symbol is also widely encountered in English-speaking countries.

Typically grammage is measured in paper mill on-line by a quality control system and verified by laboratory measurement.

Basis weight

Basis weight of paper is the density of paper expressed in terms of the mass (in pound) of a ream of paper of given dimensions and a sheet count. The American and the traditional British systems are largely the same, with only minor differences: the paper dimensions and the sheet count are different.

United States

In the US system, the weight is specified in avoirdupois pounds and the sheet count of a paper ream is usually 500 sheets. However, the mass specified is not the mass of the ream that is sold to the customer. Instead, it is the mass of the uncut "basis ream" in which the sheets have some larger size (parent size). Often, that is a size used during the manufacturing process before the paper is cut to the dimensions in which it is sold. So, to compute the mass per area, one must know

The standard dimensions and sheet count of a ream vary according to the type of paper. These "uncut" basis sizes are not normally labelled on the product, are not formally standardized, and therefore have to be guessed or inferred somehow from trading practice. Historically, this convention is the product of pragmatic considerations such as the size of a sheet mold.

By using the same basis sheet size for the same type of paper, consumers can easily compare papers of differing brands. Twenty-pound bond paper is always lighter and thinner than 32-pound bond, no matter what its cut size, and 20-pound bond letter size and 20-pound bond legal size papers are the same weight paper with a different cut size.

However, a sheet of common copy paper that has a basis weight of 20lb does not have the same mass as the same size sheet of coarse paper (newsprint). In the former case, the standard ream is 500 sheets of 17by paper, and in the latter, 500 sheets of 24by paper. Here are some basic ream sizes for various types of paper. Units are inches except where noted.

Paper typePaper size
(inches)		Sheets per ream
Bond, writing, ledger 17 Ă— 22 500
Manuscript cover 18 Ă— 31 500
Blotting 19 Ă— 24 500
Box cover 20 Ă— 24 500
Cover 20 Ă— 26 500 or 1000
Watercolour 22 Ă— 30 500
Bristol and tag Ă— 500
Tissue 24 Ă— 36 480
Newsprint 24 Ă— 36 500
Hanging, waxing, bag, etc. 24 Ă— 36 500
Book, text, offset 25 Ă— 38 500
Index bristol Ă— 500
Paperboard (all types) 12 Ă— 12 1000 (per ream)

Sheets 17by can be cut into four NaNby sheets, a standard for business stationery known conventionally as letter sized paper. So, the 17by ream became commonly used. The 25by book-paper ream developed because such a size can easily be cut into sixteen 6by book sized sheets without significant waste (nominally NaNby before trimming and binding).

Early newsprint presses printed sheets 2by in size, and so the ream dimensions for newsprint became 24by, with 500 sheets to a ream. Newsprint was made from ground wood pulp, and ground wood hanging paper (wallpaper) was made on newsprint machines. Newsprint was used as wrapping paper, and the first paper bags were made from newsprint. The newsprint ream standard also became the standard for packaging papers, even though in packaging papers kraft pulp, rather than ground wood, was used for greater strength.

Paper weight is sometimes stated using the "" symbol. For example, "20#" means "20 pounds per basis ream of that kind of paper". When the density of a ream of paper is given in pounds, it is often accompanied by its "M weight" (M is 1000 in Roman numerals). The M weight is the weight (in pounds) of 1000 cut sheets. Paper suppliers will often charge by M weight, since it is always consistent within a specific paper size, and because it allows a simple weight calculation for shipping charges.

For example, a 500-sheet ream of 20# NaNby copy paper may be specified "10 M". 1000 cut sheets (or two reams) will weigh 10lb, half of the four reams of cut paper resulting from the 20# basis ream of 17by paper.

United Kingdom

Overview of the traditional British system

Like the American system, the traditional British system also involves the use of basis weight to express the area density of paper (and, indirectly, paper thickness) in the course of buying and selling paper. The British paper industry exclusively used basis weight before 1968.[3]

In the traditional British system, basis weight is also expressed in terms of the weight of an imaginary ream of paper of a certain size. The underlying concept is that a ream of paper of the stated paper size and of the same thickness as the paper the parties are dealing with would have the stated weight. The weight is expressed in pound. As to paper sizes (basis sizes), they can, theoretically, be any sizes, but, by custom, a number of common sizes emerged. In the 1960s, even the metric A1[4] and A2[5] had been used as basis sizes alongside the British ones.

The following are common[6] [7] [8] British basis sizes (sizes of British uncut paper):

colspan="2" width="50%"
Note 1:
The Italicised writing‑paper and printing‑paper sizes were in use only prior to the 1925 standardisation[9] of writing‑paper and printing‑paper sizes. The 1925 standardisation did not apply to wrapping‑paper sizes.

Note 2:
The underlined writing‑paper and printing‑paper sizes were in use after the 1925 standardisation but were not adopted as standard sizes[10] by British Standards Institution specification number 730 of 1937.

Note 3:
The wrapping‑paper sizes marked with '*' were not adopted as standard sizes by British Standards Institution specification number 730 of 1937.

Writing paper
Atlas26 in Ă— 34 in
Copy16 in Ă— 20 in
Double elephant
(adopted by British Standards Institution specification number 730 of 1937 but not the 1925 standardisation)		27 in Ă— 40 in
Double imperial30 in Ă— 44 in
Double large post21 in Ă— 33 in
Double post
(adopted by British Standards Institution specification number 730 of 1937 but not the 1925 standardisation)		19 in Ă— 30 in
(prior to re‑definition by British Standards Institution specification number 730 of 1937, 19 in × 30 in)
Double pott15 in Ă— 25 in
Double small demy
(known as 'double demy' before the 1925 standardisation)		20 in Ă— 31 in
Double small foolscap
(known as 'double foolscap' before British Standards Institution specification number 730 of 1937)
('foolscap' is sometimes shortened to 'cap' or 'cap')		16 in Ă— 26 in
Double small royal
(known as 'double royal' before the 1925 standardisation)		24 in Ă— 38 in
Elephant23 in Ă— 28 in
Imperial22 in Ă— 30 in
Large post16 in Ă— 21 in
Pinched post14 in Ă— 18 in
Post
(adopted by British Standards Institution specification number 730 of 1937 but not the 1925 standardisation)		15 in Ă— 19 in
(prior to re‑definition by British Standards Institution specification number 730 of 1937, 15 in ×19 in)
Pott12 in Ă— 15 in
Sheet‑and‑a‑half small foolscap
(known as 'sheet‑and‑a‑half foolscap' before British Standards Institution specification number 730 of 1937)
('foolscap' is sometimes shortened to 'cap' or 'cap')		13 in Ă— 24 in
(before the 1925 standardisation, 13 in Ă— 24 in)
Sheet‑and‑a‑third small foolscap
(introduced by the 1925 standardisation)
(known as 'sheet‑and‑a‑third foolscap' before British Standards Institution specification number 730 of 1937)
('foolscap' is sometimes shortened to 'cap' or 'cap')		13 in Ă— 22 in
Small demy
(known as 'demy' before the 1925 standardisation)		15 in Ă— 20 in
Small foolscap
(known as 'foolscap' before British Standards Institution specification number 730 of 1937)
('foolscap' is sometimes shortened to 'cap' or 'cap')		13 in Ă— 16 in
Small medium
(known as 'medium' before the 1925 standardisation)		17 in Ă— 22 in
Small post
(introduced by the 1925 standardisation)		14 in Ă— 18 in
Small royal
(known as 'royal' before the 1925 standardisation)		19 in Ă— 24 in
Super royal19 in Ă— 27 in
(before the 1925 standardisation, 19 in Ă— 27 in)
Printing paper
Copy16 in Ă— 20 in
Crown15 in Ă— 20 in
Demy17 in Ă— 22 in
Double crown20 in Ă— 30 in
Double demy22 in Ă— 35 in
Double elephant
(also known as 'double large royal')
(adopted by British Standards Institution specification number 730 of 1937 but not the 1925 standardisation)		27 in Ă— 40 in
Double globe28 in Ă— 38 in
Double imperial30 in Ă— 44 in
Double foolscap
(known as 'double large foolscap' after the 1925 standardisation and before being re‑named by British Standards Institution specification number 730 of 1937)
('foolscap' is sometimes shortened to 'cap' or 'cap')		17 in Ă— 27 in
Double large post21 in Ă— 33 in
Double medium23 in Ă— 36 in
Double post
(adopted by British Standards Institution specification number 730 of 1937 but not the 1925 standardisation)		19 in Ă— 30 in
(prior to re‑definition by British Standards Institution specification number 730 of 1937, 19 in × 31 in)
Double pott15 in Ă— 25 in
Double royal25 in Ă— 40 in
Elephant23 in Ă— 28 in
Foolscap
(known as 'large foolscap' after the 1925 standardisation and before being re‑named by British Standards Institution specification number 730 of 1937)
('foolscap' is sometimes shortened to 'cap' or 'cap')		13 in Ă— 17 in
Imperial22 in Ă— 30 in
Large post16 in Ă— 21 in
Large royal
(introduced by the 1925 standardisation)		20 in Ă— 27 in
(prior to re‑definition by British Standards Institution specification number 730 of 1937, 20 in × 27 in)
Medium18 in Ă— 23 in
Music demy14 in Ă— 20 in
Post
(adopted by British Standards Institution specification number 730 of 1937 but not the 1925 standardisation)		15 in Ă— 19 in
(prior to re‑definition by British Standards Institution specification number 730 of 1937, 15 in × 19 in)
Pott12 in Ă— 15 in
Quad crown30 in Ă— 40 in
Quad demy35 in Ă— 45 in
Quad foolscap
(known as 'quad large foolscap' after the 1925 standardisation and before being re‑named by British Standards Institution specification number 730 of 1937)
('foolscap' is sometimes shortened to 'cap' or 'cap')		27 in Ă— 34 in
Quad globe38 in Ă— 56 in
Quad pott25 in Ă— 30 in
Quad royal40 in Ă— 50 in
Royal20 in Ă— 25 in
Super royal20 in Ă— 27 in
Wrapping paper
Bag cap20 in Ă— 24 in
(prior to re‑definition by British Standards Institution specification number 730 of 1937, 19 in × 24 in)
Casing36 in Ă— 46 in
(across the island of Ireland, 36 in Ă— 48 in)
Double bag cap*24 in Ă— 39 in*
Double crown20 in Ă— 30 in
Double double imperial45 in Ă— 58 in
Double elephant*31 in Ă— 46 in*
Double imperial29 in Ă— 45 in
Double medium23 in Ă— 36 in
Double small cap*25 in Ă— 34 in*
Double small hand*20 in Ă— 29 in*
Elephant*24 in Ă— 32 in*
Extra large casing40 in Ă— 48 in
Haven cap*
(sometimes called 'havon cap')		21 in Ă— 26 in*
Imperial22 in Ă— 29 in
Kent cap*18 in Ă— 21 in*
Lumber hand*17 in Ă— 22 in*
Quad crown30 in Ă— 40 in
Quad foolscap*
(known as 'quad large foolscap' after the 1925 standardisation and before British Standards Institution specification number 730 of 1937)
('foolscap' is sometimes shortened to 'cap' or 'cap')		27 in Ă— 34 in*
Quad royal*40 in Ă— 50 in*
Quad small hand*30 in Ă— 40 in*
Royal*20 in Ă— 25 in*
Saddleback36 in Ă— 45 in
Small cap*17 in Ă— 25 in*
Small hand*15 in Ă— 20 in*
(No name)20 in Ă— 24 in*
(No name)20 in Ă— 28 in*
(No name)21 in Ă— 31 in*
(No name)21 in Ă— 34 in*
(No name)22 in Ă— 32 in*
(No name)22 in Ă— 35 in*
(No name)23 in Ă— 34 in*
(No name)24 in Ă— 30 in*
(No name)24 in Ă— 36 in*
(No name)24 in Ă— 40 in*
(No name)26 in Ă— 36 in*
(No name)28 in Ă— 45 in*
(No name)29 in Ă— 44 in*
(No name)30 in Ă— 38 in*
(No name)30 in Ă— 46 in*
(No name)34 in Ă— 36 in*
(No name)36 in Ă— 36 in*
(No name)36 in Ă— 48 in*
(No name)38 in Ă— 48 in*
(No name)45 in Ă— 56 in*
One ream in the context of basis weight (basis ream) can be 480 sheets, 500 sheets, 504 sheets, or 516 sheets: there is no fixed rule on when a certain definition was applied; however, starting from the 1950s, the trend of moving towards 500 sheets emerged.

Basis weight is commonly expressed in terms of pound per ream of paper of a certain size, in the format of '[number]lb [paper size]' (e. g., '21lb large post' ('21 pounds per ream of large post paper')). Since there are basis reams of different sizes, unless the context leaves no room for ambiguity, the number of sheets in the basis ream is also given after the paper size to avoid misunderstanding: in such case, basis weight is expressed in the format of '[number]lb [paper size] [number of sheets of paper in the basis ream]', such as '21lb large post 480' ('21 pounds per 480‑sheet ream of large post paper'). In the United Kingdom, '#' has never been used to express paper weight because it is called 'hash', instead of 'pound', in British English.

Demy traditionally plays the role of the default basis size for expressing basis weights: in the British paper industry, there was a device, called 'demy scale', that was used to measure the weights of different paper samples in pound per ream of demy paper (480‑sheet, 500‑sheet, and 516‑sheet reams).[11]

Below is a list of common[12] basis weights of paper stocked by British paper merchants:

Writing paper
Common British basis weights

(various paper sizes and ream sizes)

Equivalent weight of a 500‑sheet ream of large post paper, a British uncut writing paper commonly used to express the basis weight of writing paper

(rounded to the nearest quarter)

(a common British basis for intra‑category comparison)

Equivalent weight of a 500‑sheet ream of demy paper, a British uncut printing paper commonly used by default to express the basis weight of different types of paper

(rounded to the nearest quarter)

(a common British basis for cross‑category comparison)

Equivalent grammage

(rounded to the nearest one)

Equivalent weight of a 500‑sheet ream of bond paper, an American uncut paper commonly used to express the basis weight of paper

(rounded to the nearest quarter)

(a common American basis for cross‑category comparison)

1111134612
1111124511
1212134913
1414165915
1515176316
1515176116
1515176016
1717207219
1818217620
1818207319
1817207219
1919228021
2020238522
2122248923
2121238522
2120238522
2223269324
2221248923
2324279725
2323269324
2322269324
24252810127
2423279725
25262910628
25252810127
26273011029
26252910527
27283211430
27263010929
28293311831
28273111330
30313512733
2211124511
3015176316
3015176116
3015176016
3618217620
3618207319
3617207219
4222248923
4221238522
4220238522
4421248923
1312134913
1817196818
2118217620
2119227921
2321248823
2320238322
2421248723
2523269525
2522259124
30262910628
34323612934
40354014538
1311124411
1412135113
1815176417
1815176116
2117207119
2118207319
2521238522
2823269525
2611124411
3615176116
4620228121
4619217720
4820228121
5020238422
60262910628
60252810227
70293311931
2015186417
2419228021
2419217720
2520238422
2620238322
2823269425
2822259024
2822258923
30242810026
3023269625
32252810227
34263010828
36293312132
1411134612
1411124411
2015176417
2015176116
2419217720
2418207419
2821248622
3017197018
3219227820
3218207419
3620238422
4023269425
4023269324
44252910327
46273111229
50283211731
60343913937
88252910327
100283211731
25293311831
38445018047
18293312132
4818207319
5019228021
72394416042
1822259124
20252810127
22273111129
7217207219
8422248923
29384315641
44343914137
54374215240
Printing paper
Common British basis weights

(various paper sizes and ream sizes)

Equivalent weight of a 500‑sheet ream of double crown paper, a British uncut printing paper commonly used to express the basis weight of printing paper

(rounded to the nearest quarter)

(a common British basis for intra‑category comparison)

Equivalent weight of a 500‑sheet ream of demy paper, a British uncut printing paper commonly used by default to express the basis weight of different types of paper

(rounded to the nearest quarter)

(a common British basis for cross‑category comparison)

Equivalent grammage

(rounded to the nearest one)

Equivalent weight of a 500‑sheet ream of bond paper, an American uncut paper commonly used to express the basis weight of paper

(rounded to the nearest quarter)

(a common American basis for cross‑category comparison)

1717114211
1919134612
2020134913
2019124512
2122145113
2223155414
2324155615
2322155314
2423155614
2423155514
2526176116
2524165815
2627176316
2625176016
2625165915
2728186617
2727176316
2726176316
2829196818
2827176417
2930197118
3031207319
3030197018
3029197018
3029196818
3130207219
3233227820
3231207419
3231207319
3335228121
3332217720
3433227921
3433217720
3536248522
3637248823
3636238422
3635238422
3635238221
3839269324
3837248823
3836248623
3938259124
4041279826
4040269425
4039269324
4038259124
42432810327
4241279826
44453010728
44442810327
44422810026
45473011029
45452910528
46483111229
46453010728
46442910427
47493211530
50523412232
50503211731
50493211631
50483111430
52543512733
54563713235
54523412332
55573713435
56543512733
57593913937
58583813636
60624114639
60603914137
60593913937
60583813636
61634114939
76795218649
79765017947
80835419552
80795218649
4019124512
4823155614
5026176116
5427176316
6031207319
6030197018
6029197018
6029196818
6431207319
6833217720
7036248522
7034227921
7236238422
7235238422
8040269425
8039269324
8038259124
86442910528
88442910327
96463010929
100503211731
100493211631
100483111430
120603914137
120593913937
120583813636
1422145213
1625166015
1727176316
1828186717
1827176417
1930197118
2031207419
2030197118
2029196918
2133227820
2436238522
2539269324
2641279725
28442910427
29463010828
30473111229
30442910427
32503311931
34543512633
35553613034
36573713435
44694516443
64946222159
2318124311
2519134612
2620134812
2822145213
2820134813
3023155614
3022145213
3225166015
3224155715
3223155514
3326176116
3427176316
3425166016
3425165915
3527186517
3628186717
3627186417
3627176417
3626176216
3830197118
3828186718
4031207419
4030207119
4030197118
4029196918
4233227820
4231207319
4432217620
4534228021
4533217820
4636248622
4634228021
4734228121
4838258923
4836248622
4836238522
4835238322
5039269324
5239259224
5339259224
54422810026
55432810227
5540269525
56442910427
5641279725
60473111229
60452910628
60442910427
64473111129
68543512633
69543612834
70553613034
72533512533
74583813836
80603914237
88654215240
89704616644
1928186718
2030197118
2436238522
2537248823
2536238422
2740269625
2842279926
29432810327
30452910628
3042279926
31463011029
32483111330
33463010929
34513312032
34493211530
35523412433
38533512533
40603914237
40573713535
40563613235
45684415942
48724717045
50724716844
53765017947
55835419551
4231207419
5037248823
5036238422
5035238222
5539269324
60432810227
6042279926
62452910528
64452910528
65473111029
68513312032
68493211530
69503211731
70503311931
80583813636
80563613235
2025165915
2124165715
2227186417
2328186718
2430197018
2428186717
2428186517
2529196818
2632217620
2630197118
2731207419
3037248823
3035238221
3138259124
3240269425
3341279725
34422810026
36452910528
3641279826
37463010828
38473111129
39483211430
40503211731
40473111229
40463010929
41513312032
42523412332
44553612934
45563713235
47583813836
50624114639
50593913937
50583813636
51634114939
60754917646
61765017947
66825419351
67795218749
70875720554
3219124512
3723155414
4023155614
4224165715
4628186718
4828186717
4828186517
5030197018
5029196818
5431207419
6036238422
6035238422
6035238221
6640269424
72422810026
7241279826
75452910528
80473111229
80463010929
91533412433
100593913937
100583813636
160473111229
1633227820
2041279826
27563713235
1621145113
2128186717
2230197018
2329196818
2432217720
2531207419
2635238322
2838258923
2835238322
2939269324
3040269625
3038258923
32432810227
36493211530
36453010728
38513412132
40543512834
45614014438
54734817245
67915921456
4629196818
4831207319
4931207319
5031207419
5636238522
5635238322
6039259124
6038258923
68463010828
6423155514
8029196918
8431207319
9636238522
120452910628
120442910427
3026176216
3631207419
4035238322
46432810227
50442910327
56533412433
60523412433
70664315541
1201056924865
1327186417
1429196918
22463010828
23483111330
24503311831
1628196818
1730207219
1832217620
1831207319
2138248923
2136238522
2136238522
24432810127
25452910628
26473011029
27483211430
28503311831
29523412332
30543512733
30513312132
31563613134
32573813536
34614014438
36654215240
44795218649
3630197118
60543512733
60513312132
20523412332
25463010828
25452910628
20442910528
2540269425
30483111230
67775018048
84966322660
1001147526971
1181358831784
80765018047
100966322559
1201157527071
1401348831583
3634228121
75694516343
1061157527172
1241358831784
190207136486129
1221147526971
1441358831784
220207135485129
Wrapping paper
Common British basis weights

(various paper sizes and ream sizes)

Equivalent weight of a 500‑sheet ream of double imperial paper, a British wrapping paper commonly used to express the basis weight of wrapping paper

(rounded to the nearest quarter)

(a common British basis for intra‑category comparison)

Equivalent weight of a 500‑sheet ream of demy paper, a British uncut printing paper commonly used by default to express the basis weight of different types of paper

(rounded to the nearest quarter)

(a common British basis for cross‑category comparison)

Equivalent grammage

(rounded to the nearest one)

Equivalent weight of a 500‑sheet ream of bond paper, an American uncut paper commonly used to express the basis weight of paper

(rounded to the nearest quarter)

(a common American basis for cross‑category comparison)

2881248823
401163512533
5041124411
6049145314
7057176216
8065197118
10082248823
120982910628
1401153412433
1601313914237
13299328
153410379
1943134612
2352155615
2454165915
471063211530
801815419552
1002266824465
1202728229378
3438114211
3843134612
4851155614
1201263813636
1551155614
2645134812
2946145013
3051155614
3458176316
601033111229
2001414215340
501043111229
601253713535
701454415741
1402918831483
6062186718
6567207319
8083259024
1001043111229
1201253713535
1401454415741
1601665018047
2402507526971
2401253713535
2801454415741
1956176116
3438114211
3843134612
4851155614
1440124411
1543134712
190450136486129
220450135485129
3248145314
26319338
3035103910
4250155414
1801344014538

Conversion between British basis weights, American basis weights, and grammage

It is possible to convert between different basis weights – both British and American – and grammage using different conversion formulae.

To convert between the basis weights of different paper with the same basis‑ream size (e. g., from to), the following formula can be employed:[13]

Area of one sheet of paper in the target ream Ă— Weight of the source ream Ă· Area of one sheet of paper in the source ream

To convert between the basis weights of different paper with different basis‑ream sizes (e. g., from to), the relevant formula is below:

(Number of sheets of paper in the target ream Ă— Area of one sheet of paper in the target ream) Ă— Weight of the source ream Ă· (Number of sheets of paper in the source ream Ă— Area of one sheet of paper in the source ream)

To convert between the basis weights of the same paper with different basis‑ream sizes (e. g., from to), one may either use the previous formula or the one below:

Weight of the source ream Ă— Applicable conversion factor from the table below[14]

To →From ↓480500504516
480...1.0421.051.075
5000.96...1.011.032
5040.950.992...1.022
5160.930.9690.977...
To convert from a basis weight to its equivalent grammage, the following is the applicable formula:[15]

Weight of the basis ream Ă— 703,125 Ă· Area of one sheet of paper in the basis ream in square inch Ă— Number of sheets of paper in the basis ream

To convert from grammage to the equivalent basis weight, the formula below can be used:[15]

Area of one sheet of paper in the basis ream in square inch Ă— Number of sheets of paper in the basis ream Ă— Value of gram per square metre Ă· 703,125

Utilising the aforementioned formulae, it is possible to work out the conversion factors for converting between various British and American units of basis weight and the gram per square metre:

colspan="2"
Note 1:
Value of Ă— Relevant conversion factor = Value of the unit in the left column

Note 2:
Value of a unit in the left column Ă· Relevant conversion factor = Value of

Note 3:
To convert between any two units in the left column, Value of the source unit Ă— (Conversion factor for the target unit Ă· Conversion factor for the source unit)

Note 4:
Note that, as a matter of mathematical relationship, 1 'single' unit (e. g.,) is always equal to 2 'double' unit (e. g.,) and 4 'quad' unit (e. g.,), respectively. By the same token, 1 'double' unit is always equal to 'single' unit and 2 'quad' unit, respectively; and 1 'quad' unit is always equal to 'double' unit and 'single' unit, respectively. Due to the rounding of the conversion factors in this table, calculating with the conversion factors alone may not produce such results automatically.

(UK)
(UK)1.219047
(the definition on the island of Great Britain) (UK)4.205713
(the definition on the island of Ireland) (UK)4.388570
(UK)1.523809
(UK)2
(UK)6.628570
(UK)2.742856
(UK)1.165714
(UK)3.352380
(UK)3.314285
(UK)1.759999
(UK)2.102856
(UK)1.447619
(UK)2.539681
(UK)1.574603
(UK)1.110475
(UK)4.876188
(UK)0.582857
(UK)1.676190
(UK)1.657142
(UK)0.880000
(UK)1.405713
(UK)1.051428
(UK)0.723809
(UK)3.047619
(UK)4
(UK)2.331429
(UK)1.269840
(UK)4.114285
(UK)0.832857
(UK)0.740317
(UK)0.787301
(UK)0.555237
(UK)1.158094
(metric)3.571142
(US)0.949841
(US)1.628571
(US)1.320634
(US)1.975236
(US)2.194284
(US)2.412696
colspan="2"
Note 1:
Value of Ă— Relevant conversion factor = Value of the unit in the left column

Note 2:
Value of a unit in the left column Ă· Relevant conversion factor = Value of

Note 3:
To convert between any two units in the left column, Value of the source unit Ă— (Conversion factor for the target unit Ă· Conversion factor for the source unit)

Note 4:
Note that, as a matter of mathematical relationship, as long as the ream size is the same, 1 'single' unit (e. g.,) is always equal to 2 'double' unit (e. g.,) and 4 'quad' unit (e. g.,), respectively. By the same token, 1 'double' unit is always equal to 'single' unit and 2 'quad' unit, respectively; and 1 'quad' unit is always equal to 'double' unit and 'single' unit, respectively. Due to the rounding of the conversion factors in this table, calculating with the conversion factors alone may not produce such results automatically.

(UK)
(UK)2.155275
(UK)2.245079
(UK)2.263039
(UK)2.316921
(the pre–‍1937 standardisation definition) (UK)1.141027
(the pre–‍1937 standardisation definition) (UK)1.188571
(the pre–‍1937 standardisation definition) (UK)1.198079
(the pre–‍1937 standardisation definition) (UK)1.226605
(UK)1.170285
(UK)1.219047
(UK)1.228799
(UK)1.258056
(definition on the island of Great Britain) (UK)4.037483
(definition on the island of Great Britain) (UK)4.205713
(definition on the island of Great Britain) (UK)4.239357
(definition on the island of Great Britain) (UK)4.340294
(definition on the island of Ireland) (UK)4.213026
(definition on the island of Ireland) (UK)4.388570
(definition on the island of Ireland) (UK)4.423677
(definition on the island of Ireland) (UK)4.529003
(UK)0.804571
(UK)0.838095
(UK)0.844799
(UK)0.864914
(UK)0.731428
(UK)0.761905
(UK)0.768000
(UK)0.786285
(UK)0.960000
(UK)1.008000
(UK)1.032000
(UK)2.282055
(UK)2.377142
(UK)2.396159
(UK)2.453210
(UK)1.462856
(UK)1.523809
(UK)1.535999
(UK)1.572571
(UK)1.919999
(UK)2
(UK)2.015999
(UK)2.063999
(UK)6.363425
(UK)6.628570
(UK)6.681596
(UK)6.840682
(UK)2.633141
(UK)2.742856
(UK)2.764798
(UK)2.830627
(UK)3.476721
(UK)3.621586
(UK)3.650557
(UK)3.737475
(UK)1.119085
(UK)1.165714
(UK)1.175040
(UK)1.203017
(UK)2.594132
(UK)2.702221
(UK)2.723838
(UK)2.788691
(UK)3.218284
(UK)3.352380
(UK)3.379198
(UK)3.459655
(UK)3.181712
(UK)3.314285
(UK)3.340798
(UK)3.420341
(UK)1.689599
(UK)1.759999
(UK)1.774079
(UK)1.816319
(UK)2.018741
(UK)2.102856
(UK)2.119678
(UK)2.170147
(the pre–‍1937 standardisation definition) (UK)1.412875
(the pre–‍1937 standardisation definition) (UK)1.471745
(the pre–‍1937 standardisation definition) (UK)1.483518
(the pre–‍1937 standardisation definition) (UK)1.518840
(the pre–‍1937 standardisation definition) (UK)1.454932
(the pre–‍1937 standardisation definition) (UK)1.515555
(the pre–‍1937 standardisation definition) (UK)1.527679
(the pre–‍1937 standardisation definition) (UK)1.564052
(UK)1.389714
(UK)1.447619
(UK)1.459199
(UK)1.493942
(UK)0.914285
(UK)0.952380
(UK)0.959999
(UK)0.982856
(UK)2.438093
(UK)2.539681
(UK)2.559998
(UK)2.620950
(UK)2.072379
(UK)2.158729
(UK)2.175998
(UK)2.227808
(UK)1.511618
(UK)1.574603
(UK)1.587199
(UK)1.624990
(UK)1.066056
(UK)1.110475
(UK)1.119359
(UK)1.146010
(UK)1.414095
(UK)1.473016
(UK)1.484799
(UK)1.520152
(UK)2.223541
(UK)2.316189
(UK)2.334718
(UK)2.620950
(UK)1.570132
(UK)1.635555
(UK)1.648639
(UK)1.687892
(UK)1.872456
(UK)1.950475
(UK)1.966078
(UK)2.012890
(UK)4.681139
(UK)4.876188
(UK)4.915196
(UK)5.032225
(UK)0.559543
(UK)0.582857
(UK)0.587520
(UK)0.601508
(UK)1.331199
(UK)1.386666
(UK)1.397759
(UK)1.431039
(UK)1.609142
(UK)1.676190
(UK)1.689599
(UK)1.729827
(UK)1.590856
(UK)1.657142
(UK)1.670399
(UK)1.710170
(UK)0.959999
(UK)0.999999
(UK)1.007999
(UK)1.031999
(UK)0.844799
(UK)0.880000
(UK)0.887039
(UK)0.908159
(the pre–‍1937 standardisation definition) (UK)1.316571
(the pre–‍1937 standardisation definition) (UK)1.371428
(the pre–‍1937 standardisation definition) (UK)1.382399
(the pre–‍1937 standardisation definition) (UK)1.415314
(UK)1.349484
(UK)1.405713
(UK)1.416958
(UK)1.450696
(UK)0.960000
(UK)1
(UK)1.008000
(UK)1.032000
(UK)1.009371
(UK)1.051428
(UK)1.059839
(UK)1.085073
(UK)0.727238
(UK)0.757540
(UK)0.763600
(UK)0.781781
(UK)0.665295
(UK)0.693016
(UK)0.698559
(UK)0.715192
(the pre–‍1925 standardisation definition) (UK)0.706437
(the pre–‍1925 standardisation definition) (UK)0.735872
(the pre–‍1925 standardisation definition) (UK)0.741759
(the pre–‍1925 standardisation definition) (UK)0.759420
(the pre–‍1925 standardisation definition) (UK)0.727466
(the pre–‍1925 standardisation definition) (UK)0.757777
(the pre–‍1925 standardisation definition) (UK)0.763839
(the pre–‍1925 standardisation definition) (UK)0.782026
(UK)0.694857
(UK)0.723809
(UK)0.729600
(UK)0.746971
(UK)0.457143
(UK)0.476191
(UK)0.480000
(UK)0.491429
(UK)2.925713
(UK)3.047619
(UK)3.071998
(UK)3.145141
(UK)3.839999
(UK)4
(UK)4.031999
(UK)4.127999
(UK)2.238171
(UK)2.331429
(UK)2.350080
(UK)2.406034
(UK)5.188263
(UK)5.404442
(UK)5.447676
(UK)5.577383
(UK)1.828572
(UK)1.904763
(UK)1.920000
(UK)1.965715
(UK)4.876186
(UK)5.079362
(UK)5.119995
(UK)5.241900
(UK)2.925712
(UK)3.047618
(UK)3.071998
(UK)3.145140
(UK)1.219046
(UK)1.269840
(UK)1.279999
(UK)1.310475
(UK)3.949712
(UK)4.114285
(UK)4.147198
(UK)4.245940
(the pre–‍1925 standardisation definition) (UK)0.791466
(the pre–‍1925 standardisation definition) (UK)0.824444
(the pre–‍1925 standardisation definition) (UK)0.831040
(the pre–‍1925 standardisation definition) (UK)0.850826
(UK)0.799543
(UK)0.832857
(UK)0.839520
(UK)0.859508
(UK)0.710704
(UK)0.740317
(UK)0.746240
(UK)0.764007
(UK)1.036190
(UK)1.079364
(UK)1.087999
(UK)1.113904
(UK)0.755809
(UK)0.787301
(UK)0.793599
(UK)0.812495
(UK)0.533028
(UK)0.555237
(UK)0.559679
(UK)0.573005
(UK)0.731428
(UK)0.761905
(UK)0.768000
(UK)0.786285
(UK)0.938666
(UK)0.977777
(UK)0.985599
(UK)1.009066
(UK)0.654018
(UK)0.681269
(UK)0.686719
(UK)0.703070
(UK)1.111770
(UK)1.158094
(UK)1.167359
(UK)1.195153
(the pre–‍1925 standardisation definition) (UK)1.267199
(the pre–‍1925 standardisation definition) (UK)1.319999
(the pre–‍1925 standardisation definition) (UK)1.330559
(the pre–‍1925 standardisation definition) (UK)1.362239
(the pre–‍1925 standardisation definition) (UK)1.374475
(the pre–‍1925 standardisation definition) (UK)1.431745
(the pre–‍1925 standardisation definition) (UK)1.443199
(the pre–‍1925 standardisation definition) (UK)1.477561
(UK)1.250742
(UK)1.302856
(UK)1.313279
(UK)1.344547
(UK)1.170285
(UK)1.219047
(UK)1.228799
(UK)1.258056
(UK)1.365333
(UK)1.422222
(UK)1.433599
(UK)1.467733
(UK)1.587199
(UK)1.653333
(UK)1.666559
(UK)1.706239
(UK)1.740799
(UK)1.813333
(UK)1.827839
(UK)1.871359
(UK)1.716418
(UK)1.787936
(UK)1.802239
(UK)1.845149
(UK)1.877332
(UK)1.955555
(UK)1.971198
(UK)2.018132
(UK)1.906589
(UK)1.986031
(UK)2.001918
(UK)2.049583
(UK)1.755427
(UK)1.828571
(UK)1.843199
(UK)1.887084
(UK)2.106512
(UK)2.194284
(UK)2.211838
(UK)2.264501
(UK)2.340569
(UK)2.438094
(UK)2.457598
(UK)2.516112
(UK)2.282056
(UK)2.377142
(UK)2.396159
(UK)2.453210
(UK)3.071998
(UK)3.199999
(UK)3.225598
(UK)3.302398
(UK)3.111008
(UK)3.240634
(UK)3.266558
(UK)3.344333
(UK)2.779426
(UK)2.895237
(UK)2.918398
(UK)2.987883
(UK)3.364569
(UK)3.504761
(UK)3.532798
(UK)3.616912
(UK)2.984227
(UK)3.108571
(UK)3.133438
(UK)3.208044
(UK)3.159770
(UK)3.291428
(UK)3.317758
(UK)3.396752
(UK)4.213026
(UK)4.388570
(UK)4.423677
(UK)4.529003
(UK)4.447083
(UK)4.632379
(UK)4.669437
(UK)4.780614
(UK)6.143996
(UK)6.399998
(UK)6.451196
(UK)6.604796
(metric)3.571142
(US)0.949841
(US)1.628571
(US)1.320634
(US)1.975236
(US)2.194284
(US)2.412696
Using British basis sizes and the 500‑sheet basis‑ream (a traditional British basis‑ream size that coincides with the modern standard definition of 'ream'), and with the help of the aforementioned conversion formulae or conversion factors, it is possible to express the paper weights of different types of paper in everyday life using British units of basis weight: the typical photocopier paper that is used as all‑purpose paper is 17 or 19 (70 or 80gsm);[16] personal and business letter paper, especially that with engraved letterheads, is typically 24–29 (100–120gsm);[17] greetings cards are usually 85–106 (200–250gsm);[18] newspaper paper is typically 15–23 (35–55gsm);[19] business cards are usually 128–149 (300–350gsm);[19] two‑ply toilet rolls and paper kitchen towels are 7 (31gsm) (both layers combined) and 17 (40gsm), respectively; and the typical department‑store wrapping paper is commonly 46–65 (50–70gsm). In the traditional British system, large post, double crown, and double imperial are common British basis sizes for writing paper, printing paper and other paper that is not writing or wrapping paper, and wrapping paper, respectively. '500' is omitted because it is clear from the context that a 'ream' is 500 sheets.

Caliper

Paper thickness, or caliper, is a common measurement specified and required for certain printing applications. Since a paper's density is typically not directly known or specified, the thickness of any sheet of paper cannot be calculated by any method. Instead, it is measured and specified separately as its caliper. However, paper thickness for most typical business papers might be similar across comparable brands. If thickness is not specified for a paper in question, it must be either measured or guessed based on a comparable paper's specification.

Caliper is usually measured in micrometres (ÎĽm), or in the United States also in mils (1 mil =  in = 25.4 ÎĽm). Commonly, 20-pound bond paper ranges between roughly in thickness.[20]

The paper density is calculated by dividing the grammage over the caliper, and is usually expressed in grams per cubic centimetre (g/cm3)[21] to cancel out the mathematical need for unit conversions between metres and micrometres (a conversion factor of 1,000,000).

See also

External links

Notes and References

  1. International Standard ISO 536: Paper and board – Determination of grammage. International Organization for Standardization, Geneva.
  2. Web site: ISO 536:2019 . 2022-10-05 . ISO . en.
  3. Web site: Highlight . 11 . January, 1968.
  4. Page 3, July, 1967 edition, Highlight
  5. Page 3, October, 1967 edition, Highlight
  6. Pages 136, 138, and 142, Paper and Its Uses (1919 edition)
  7. Pages 148, 150, and 171–173, Paper and Its Uses (1939 edition)
  8. [iarchive:papermakerspocke00beverich/page/28/mode/2up|Page 29]
  9. [iarchive:dli.ernet.18571/page/168/mode/2up|Page 168]
  10. [iarchive:dli.ernet.18571/page/170/mode/2up|Pages 171–173]
  11. [iarchive:paperitsusestrea00daweuoft/page/96/mode/2up|Pages 96 and 97]
  12. Based on the basis weights mentioned in the paper‑related advertisements and articles in the following newspapers and paper‑industry magazines published during the days when the British paper industry exclusively used basis weights:
  13. https://babel.hathitrust.org/cgi/pt?id=uc1.d0001467554&seq=536 Page 368
  14. [iarchive:paperitsusestrea00daweuoft/page/148/mode/2up|Page 148]
  15. [iarchive:dli.ernet.18571/page/156/mode/2up|Page 157]
  16. Web site: GSM Paper: the Complete Guide . 10 February 2025 . 19 January 2025 . https://web.archive.org/web/20250119103612/https://colourgraphics.com/blog/what-is-gsm-paper/#mcetoc_1hdlpjhi122 . dead .
  17. Web site: What is GSM Paper Weight? . Solopress Blog.
  18. Web site: Understanding the Different gsm Weights for Card and Paper Supplies . Mankey Monkey.
  19. Web site: Paper GSM Guide . The Paperbox Limited.
  20. Web site: Paper Comparisons. https://web.archive.org/web/20121022063704/http://www.havilandprinting.com/papercomparisons/. dead. 22 October 2012. 22 October 2012.
  21. Web site: ISO 534:2011(en) Paper and board — Determination of thickness, density and specific volume.

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