A4 size in mm
A4 paper is exactly 210 × 297 mm. That is the ISO 216 definition — millimetres are how the standard is written, so these are the precise figures.
210 mmwidth
297 mmheight
ISO 216standard
The A series in millimetres
| Size | Millimetres |
|---|---|
| A0 | 841 × 1189 mm |
| A1 | 594 × 841 mm |
| A2 | 420 × 594 mm |
| A3 | 297 × 420 mm |
| A4 | 210 × 297 mm |
| A5 | 148 × 210 mm |
| A6 | 105 × 148 mm |
| A7 | 74 × 105 mm |
Why 210 × 297?
Every A size has the same aspect ratio, 1:√2 (about 1:1.414). Halving an A3 along its long edge gives exactly two A4 sheets with identical proportions. The series starts at A0, which is one square metre in area — from there each size is the previous one folded in half. That is why the numbers look arbitrary but the system is not.
The 1:√2 ratio is the reason scaling A4 to A3 on a photocopier fills the page perfectly with no cropping — a trick US Letter cannot do, because its proportions change from size to size.
Frequently asked questions
What is A4 size in mm?
Exactly 210 × 297 mm.
Is A4 exactly 210 mm wide?
Yes — ISO 216 defines A4 as 210 mm by 297 mm exactly, with a manufacturing tolerance of about ±1.5 mm.
What is A3 in mm?
297 × 420 mm — exactly twice the area of A4.