Half the last

The ISO B series

B sizes fill the gaps between A sizes: each B is the geometric mean of the A size with the same number and the one above it. B4 is the sheet halfway, in proportion, between A4 and A3.

B0 to B10

ISO B series, millimetres, width × height. Bars show height to scale.
SizemmTypical use
B01000 × 1414
B1707 × 1000
B2500 × 707
B3353 × 500
B4250 × 353Newspapers
B5176 × 250Books
B6125 × 176Books
B788 × 125
B862 × 88Playing cards
B944 × 62
B1031 × 44
How exact is a B sheet?

ISO 216 allows ±1.5 mm on dimensions up to 150 mm, ±2 mm from 150 to 600 mm, and ±3 mm above that. The older German standard, DIN 476, was stricter: ±1, ±1.5 and ±2 mm for the same ranges.1

ISO B and JIS B are not the same

Japan’s JIS P 0138 uses the same A series but a different B series. Its B sizes take the arithmetic mean of neighbouring A areas, not the geometric mean, so a Japanese B5 is 182 × 257 mm against ISO B5’s 176 × 250. 1

The A series → The C series → ← Why √2