International Paper Sizes
The A series is for general printed matters including stationery and publications. The basic standard sheet, A0 measures 841 x 1189 mm which is 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 A0, A2 is one quarter of A0, and A3 is an eighth of the A0 sheet area, etc. Sheet sizes larger than A0 retain the same proportions and a designating numeral is prefixed to the letter. Thus 2A0 indicates a sheet twice as large as A0.
The B series is about half way between two A sizes. It is intended as an alternative to the A series. It is used primarily for posters, wall charts and similar pieces where the difference in size of the larger sheets in the A series represents too large a jump. The basic B size, called B0. measures 1000 x 1414 mm.
The C series is used for folders, post cards, and envelopes. The C series of envelope sizes is suitable for insertion of A series sizes either flat or folded: A C6 envelope will take an A6 sheet flat, and A5 folded once, or an A4 sheet folded twice.