Paper sizes (ISO A series & Letter)
Each ISO A size is half the next larger one — the long side is halved each step down (A4 is the office default in most countries; US Letter ≈ 8.5 × 11 in).
| Size | mm | inches (approx) |
|---|---|---|
| A0 | 841 × 1189 | 33.1 × 46.8 |
| A1 | 594 × 841 | 23.4 × 33.1 |
| A2 | 420 × 594 | 16.5 × 23.4 |
| A3 | 297 × 420 | 11.7 × 16.5 |
| A4 | 210 × 297 | 8.27 × 11.7 |
| A5 | 148 × 210 | 5.83 × 8.27 |
| A6 | 105 × 148 | 4.13 × 5.83 |
| Letter (US) | 216 × 279 | 8.5 × 11 |
| Legal (US) | 216 × 356 | 8.5 × 14 |
| Tabloid / Ledger | 279 × 432 | 11 × 17 |
Notes
- Printer margins reduce usable area.
- B-series and Japanese B sizes are different standards.
Why A4 and US Letter are different sizes
A4 measures 210 × 297 mm (about 8.27 × 11.7 in) while US Letter is 216 × 279 mm (8.5 × 11 in) — Letter is a fraction wider and visibly shorter. The A series comes from a 1922 German standard (DIN 476) built on a single elegant rule: the aspect ratio is the square root of 2, so folding a sheet in half along its long side preserves the shape. A0 starts at just over one square meter (841 × 1189 mm), and every halving steps down one letter. Letter grew out of American papermaking practice in inches and was formalized much later, and the US never adopted the metric standard.
The halving trick and the whole A series
Because each size is exactly half the area of the next size up, the A series scales like no other system: two A4 sheets side by side make an A3, four make an A2, and sixteen A6 cards tile a single A0. The chart traces the ladder from A0 (841 × 1189 mm) through A4 (210 × 297 mm) down to A6 (105 × 148 mm). Photocopiers exploit this: a 71 percent reduction shrinks an A3 page perfectly onto A4, and 141 percent enlarges it back. The same math lets designers work at A3 and print proofs at A4 without recomposing a single element — one reason the standard spread through ISO 216 to nearly every country.
Printer margins: why the printable area shrinks
The dimensions in the chart are the sheet, not what you can print on. Every printer has a mechanical dead zone — typically 3 to 6 mm on each edge — where rollers grip and the head cannot reach, so a full-bleed A4 design loses several millimeters on all sides unless you print on oversized stock and trim. When a US Letter document is printed on A4 (or the reverse), software must either scale the content down slightly or crop it; A4's extra length eats the bottom margin, while Letter's extra width nudges the sides. Setting the correct paper size before layout avoids clipped footers and shifted headers entirely.
Choosing between Letter, Legal, and Tabloid
The US lineup covers three everyday formats: Letter (216 × 279 mm) for correspondence, Legal (216 × 356 mm) whose extra 3 inches suit contracts and pleadings, and Tabloid/Ledger (279 × 432 mm, i.e. 11 × 17 in) for spreads, newsletters, and posters — folded in half, a Tabloid sheet yields four Letter pages. Most of the world defaults to A4 for office work, reserving A3 for diagrams and A5 or A6 for flyers and cards. If documents must cross the Atlantic, keep critical content 10 mm inside the trim: that safety zone fits inside both A4 and Letter, so nothing is lost whichever sheet the recipient prints on.
Frequently asked questions
- Is A4 the same as US Letter?
- No — A4 is 210 × 297 mm (8.27 × 11.7 in), slightly narrower and taller than US Letter at 216 × 279 mm (8.5 × 11 in).
- What size is A4 paper in mm?
- A4 measures 210 × 297 mm, or about 8.27 × 11.7 inches.
- How do A-series paper sizes relate to each other?
- Each A size is half the area of the next size up: cutting an A3 sheet in half along its long side gives two A4 sheets.