Paper sizes are one of the most common places where metric and inch measurements collide. Most of the world uses ISO sizes such as A4, which are defined in millimeters. The US and Canada use Letter and Legal, which are defined in inches. This guide lists both systems with exact conversions, so you can set up documents, frames and printers correctly.
A-Series Paper Sizes in Inches (ISO 216)
| Size | Millimeters | Inches | Common use |
|---|---|---|---|
| A0 | 841 × 1189 mm | 33.11 × 46.81 in | Posters, technical drawings |
| A1 | 594 × 841 mm | 23.39 × 33.11 in | Posters, flip charts |
| A2 | 420 × 594 mm | 16.54 × 23.39 in | Posters, drawings |
| A3 | 297 × 420 mm | 11.69 × 16.54 in | Diagrams, small posters |
| A4 | 210 × 297 mm | 8.27 × 11.69 in | Standard letters and documents |
| A5 | 148 × 210 mm | 5.83 × 8.27 in | Notebooks, flyers |
| A6 | 105 × 148 mm | 4.13 × 5.83 in | Postcards |
Why A-Series Sizes Are So Clever
Every A size has the same proportions: the long side is √2 (about 1.414) times the short side. Fold any A sheet in half across its long side and you get the next size down with exactly the same shape — two A4 sheets make one A3, two A3 sheets make one A2, and so on. A0 has an area of one square meter, which is why its dimensions (841 × 1189 mm) look unusual.
That fixed ratio means you can enlarge A4 to A3 on a photocopier (141%) or reduce A3 to A4 (71%) without cropping or leaving empty margins.
US Paper Sizes in Millimeters
| Size | Inches | Millimeters | Common use |
|---|---|---|---|
| Letter | 8.5 × 11 in | 215.9 × 279.4 mm | Standard US documents |
| Legal | 8.5 × 14 in | 215.9 × 355.6 mm | Contracts, legal forms |
| Tabloid / Ledger | 11 × 17 in | 279.4 × 431.8 mm | Newsletters, spreadsheets |
| Half Letter | 5.5 × 8.5 in | 139.7 × 215.9 mm | Booklets, notepads |
A4 vs US Letter: The Difference That Causes Printing Problems
A4 (210 × 297 mm) and US Letter (215.9 × 279.4 mm) look almost identical, but:
- Letter is 5.9 mm wider than A4.
- A4 is 17.6 mm taller than Letter.
If a document set up for A4 is printed on Letter paper, the bottom of the page is usually cut off or the printer shrinks it. Going the other way, a Letter document on A4 paper gets narrow side margins trimmed. Before printing, check the page size in your document settings and in the printer dialog — both need to match the paper in the tray.
Photo Print Sizes in Millimeters
| Print size | Millimeters |
|---|---|
| 4 × 6 in | 101.6 × 152.4 mm |
| 5 × 7 in | 127.0 × 177.8 mm |
| 8 × 10 in | 203.2 × 254.0 mm |
Photo sizes are sold in inches almost everywhere, even in metric countries — a “10 × 15 cm” print is the metric name for roughly the same 4 × 6 in print (101.6 × 152.4 mm).
How to Convert Any Paper Size
- mm to inches: divide each side by 25.4. A5 short side: 148 ÷ 25.4 = 5.83 in.
- inches to mm: multiply by 25.4. Letter width: 8.5 × 25.4 = 215.9 mm.
Use the mm to inches converter for any size not listed here, or our large sizes page for more everyday examples.
Frequently Asked Questions
What is A4 in inches?
A4 is 210 × 297 mm, which is 8.27 × 11.69 inches.
Is A4 bigger than Letter?
A4 is taller (by 17.6 mm) but narrower (by 5.9 mm). Its total area is slightly larger.
What size is A3 in inches?
A3 is 297 × 420 mm, or 11.69 × 16.54 inches. Compared with US Tabloid (11 × 17 in), A3 is about 0.7 in wider but 0.46 in shorter.
Related: How to read a tape measure · MM to Inches chart (printable) · Large sizes in inches