Guide
Paper sizes in inches and mm: A4, Letter, Legal, A0 to A6
Every common paper size in both units, the logic behind the A-series, and the scaling numbers for printing A4 on Letter and back.
By Buğra SözeriPublished
If you need the exact size of A4, Letter or any other common sheet in millimeters or inches, the tables below have it. ISO sizes are defined in millimeters and US sizes in inches, so each table shows the defining unit first and the converted one second. After that: why A4 and Letter don't match, and the scale to use when you print one on the other.
A-series paper sizes (ISO 216)
| Size | Millimeters | Inches |
|---|---|---|
| A0 | 841 × 1189 mm | 33.11 × 46.81 in |
| A1 | 594 × 841 mm | 23.39 × 33.11 in |
| A2 | 420 × 594 mm | 16.54 × 23.39 in |
| A3 | 297 × 420 mm | 11.69 × 16.54 in |
| A4 | 210 × 297 mm | 8.27 × 11.69 in |
| A5 | 148 × 210 mm | 5.83 × 8.27 in |
| A6 | 105 × 148 mm | 4.13 × 5.83 in |
US paper sizes: Letter, Legal and Tabloid
| Size | Inches | Millimeters |
|---|---|---|
| Letter (ANSI A) | 8.5 × 11 in | 215.9 × 279.4 mm |
| Legal | 8.5 × 14 in | 215.9 × 355.6 mm |
| Tabloid / Ledger (ANSI B) | 11 × 17 in | 279.4 × 431.8 mm |
Why the A-series numbers look odd
The A-series is built on one rule: every sheet has sides in the ratio 1 : √2. Fold such a sheet in half across its long side and the half has the same shape as the whole. A0 is set to an area of roughly one square meter (841 × 1189 mm = 0.9999 m²), and each smaller size is the previous one cut in half, rounded to the whole millimeter. That is why A4 is exactly half of A3 and why an A3 printout reduced to 70% fits on A4 with nothing cut off.
US sizes come from a different tradition. Letter (8.5 × 11 in) has a ratio of 1.294, and Legal (8.5 × 14 in) is Letter made longer. Tabloid is two Letter sheets side by side, so Letter does halve neatly into Tabloid, but Legal fits no halving series at all.
A4 vs Letter: what changes when you print
A4 is 8.27 × 11.69 in. Letter is 8.5 × 11 in. So A4 is 0.23 in narrower and 0.69 in taller. Print an A4 PDF on Letter at 100% and the bottom margin gets cut. Print a Letter PDF on A4 and the sides get cut.
Worked example: fitting A4 onto Letter
To fit without cropping, the scale has to satisfy both sides. Width allows 215.9 ÷ 210 = 1.028, height allows 279.4 ÷ 297 = 0.941. The smaller wins, so set the printer to 94%. The other way round, Letter onto A4 needs 97%. Most print dialogs have a "fit to page" option that does this for you, but it often adds the printer's own margin on top, so the result can be a little smaller still.
Our view: if a document will be printed on both sides of the Atlantic, design it with a 20 mm margin on every edge. Then it survives on either paper size at 100% with nothing lost. For images and posters, work out the pixels you need with the DPI calculator or our guide to print sizes in pixels at 300 DPI.
Frequently asked questions
- What is A4 size in inches?
- A4 is 210 × 297 mm, which is 8.27 × 11.69 inches.
- What is US Letter size in mm?
- US Letter is 8.5 × 11 inches, which is 215.9 × 279.4 mm.
- Is A4 bigger than Letter?
- A4 is 17.6 mm taller but 5.9 mm narrower than Letter. Neither fits the other exactly, which is why documents get cropped or gain margins when printed on the other size.
- Why is A4 210 × 297 mm?
- A-series sheets keep a 1 : √2 ratio, so cutting one in half gives the next size with the same shape. A0 is defined as about 1.00 m², and A4 is A0 halved four times.
Sources & references
Authoritative references cited by this piece. Verified by Buğra Sözeri on the dates shown and re-checked at every deploy.
- ISO 216 — Writing paper and certain classes of printed matter: trimmed sizes, A and B series — Defines the A-series sizes in millimeters(as of )
- ASME Y14.1 — Decimal Inch Drawing Sheet Size and Format — Defines ANSI A (Letter) and ANSI B (Tabloid) sheet sizes in inches(as of )
- NIST Handbook 44, Appendix C — Units and Systems of Measurement — The inch as exactly 25.4 mm(as of )
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Published October 17, 2026