Guide

Preparing paper sizes and print

The A series follows a single rule: every format is created by halving the next larger one. That produces the constant aspect ratio of 1 to the square root of 2.

The halving rule

A0 has an area of exactly one square metre and measures 841 × 1189 mm. Halving A0 along the long side gives A1 at 594 × 841 mm, then A2 at 420 × 594 mm and so on down to A10. Because the aspect ratio stays constant, any document can be scaled between two A formats without distortion — which is exactly what the series was designed for.

B series and C series

The B series is larger than the A series with the same number and is used for books, posters and signage. The C series is intended for envelopes and matches the A format of the same number: a C4 envelope takes an unfolded A4 sheet, a C5 envelope an A5 sheet or a folded A4 sheet.

US formats and why they do not fit

US Letter measures 216 × 279 mm and has an aspect ratio of 8.5 to 11, not 1 to the square root of 2. Legal and Tabloid follow the same logic. A document set for Letter loses margin or content when printed on A4 because the proportions differ, and A4 on Letter leaves a margin strip. For exchange between the two systems, converting to millimetres is the most reliable route.

Resolution and typography in print

For print data, pixel figures are only meaningful together with the resolution. A 300 dpi print of A4 requires about 2480 × 3508 pixels. For type: the point is a physical length unit with 72 points per inch, whereas a CSS pixel is a reference unit with 96 pixels per inch. One CSS pixel therefore equals 0.75 points.

Matching conversions

Matching tables

Sources