Field note 03

An A4 sheet measures 210 × 297 mm, which is 21 × 29.7 cm or about 8.27 × 11.69 inches. It is the standard office paper in almost every country except the US, Canada and a few others that use Letter.

Where the odd numbers come from

The A series, defined in ISO 216, starts from A0, a sheet with an area of exactly one square meter and sides in the ratio 1 : √2. Cut it in half across the long side and you get A1 with the same proportions; halve again for A2, then A3, then A4. That is why A4 is 1/16 of a square meter and why an A4 folded in half is exactly an A5 (148 × 210 mm).

A4 next to US Letter

Letter is 8.5 × 11 in, or 215.9 × 279.4 mm. Compared with A4 it is about 6 mm wider and 18 mm shorter. Documents laid out for one often clip or leave a white band on the other, so set the paper size before printing. The paper size chart lists both families side by side.

A4 in pixels

• 300 DPI (print quality): 2480 × 3508 px
• 150 DPI: 1240 × 1754 px
• 96 DPI (common screen setting): 794 × 1123 px
• 72 DPI (PDF points): 595 × 842

For other formats and resolutions, use paper size in pixels.

Handy A4 facts

• A sheet of ordinary 80 g/m² paper weighs about 5 g.
• A C4 envelope (229 × 324 mm) holds A4 flat; a DL envelope (110 × 220 mm) takes A4 folded in three.
• The short side, 21 cm, makes a decent stand-in ruler when nothing else is around.