There is a standardised system of related sheet sizes, based on a series of three different sizes called A, B or C - all of the same proportions.

All sizes have the rectangular proportion of 1:sqrt2 (or 1: 1414) which is mathematically unique - no other size allows paper to be cut, or folded, in half and yet retain the same proportion.

Because these proportions always remain constant, artwork will enlarge or reduce photographically to fit any International Size. It is also not necessary to give dimensions of paper, as descriptions such as A4 or A3 are in universal use.

Definition of weight, or "substance", of paper is expressed in constant terms as "grams per square metre" (or gsm); if a sheet of AO paper weighs 90 grams it is then described as "90 gsm", regardless of the actual size of the sheet.

The A Series

The series is for general printed matter including stationery and publications. The basic standard sheet AO measures 841 x 1189mm which is the equivalent of a square metre in area. Each number after the series initial A indicates a halving of the preceding larger area. Thus A1 is half of AO, A2 is one-quarter of AO, A3 is an eighth of the AO sheet area, etc. Sheet sizes larger than AO retain the same proportions and a designating numeral is prefixed to the letter. Thus 2A0 indicates a sheet twice as large as AO.

1682 x 2378

A4

210 x 297

1189 x 1682

148 x 210

841 x 1189

105 x 148

594 x 841

74 x 105

420 x 594

52 x 74

297 x 420

37 x 52

BO 

1000 x 1414

B5 

176 x 250

707 x 1000

125 x 177

500 x 707

88 x 125

353 x 500

62 x 88

250 x 353

44 x 62