A4 paper is 210 × 297 mm (8.3 × 11.7 inches). US Letter paper is 8.5 × 11 inches (215.9 × 279.4 mm). So A4 is a little narrower and a little taller than Letter. Most of the world uses A4. The United States and Canada mostly use Letter.
A4 belongs to the A series, set by the international standard ISO 216. Letter, Legal and Ledger (Tabloid) are North American sizes measured in inches. This guide gives you a full paper size chart in millimetres, centimetres and inches, shows how the A sizes fit together, and explains what to do when you print an A4 file on Letter paper or the other way round.
Paper sizes at a glance
- A4: 210 × 297 mm (8.3 × 11.7 in). The everyday size in most countries.
- Letter: 8.5 × 11 in (215.9 × 279.4 mm). The everyday size in the US and Canada.
- Legal: 8.5 × 14 in (215.9 × 355.6 mm). Same width as Letter, but longer.
- A3: 297 × 420 mm (11.7 × 16.5 in). Two A4 sheets side by side.
- Ledger / Tabloid: 11 × 17 in (279.4 × 431.8 mm). Two Letter sheets side by side.
- A5: 148 × 210 mm (5.8 × 8.3 in). Half of A4, a common notebook size.
What is the difference between A4 and Letter?
A4 is 5.9 mm (about 0.23 in) narrower than Letter and 17.6 mm (about 0.69 in) taller. Overall, an A4 sheet has about 3% more paper than a Letter sheet. The shapes are different too: A4 is long and slim, while Letter is a bit wider and shorter.
| A4 | US Letter | |
|---|---|---|
| Size in mm | 210 × 297 | 215.9 × 279.4 |
| Size in inches | 8.27 × 11.69 | 8.5 × 11 |
| Size in cm | 21 × 29.7 | 21.59 × 27.94 |
| Area | 0.0624 m² | 0.0603 m² |
| Shape (long side ÷ short side) | 1.414 | 1.294 |
| Standard | ISO 216 | North American inch sizes |
| Main users | Most of the world | US and Canada |
Is A4 bigger than Letter? It depends on what you mean. A4 is taller and has slightly more area, but Letter is wider. Neither sheet fits fully inside the other.
How the A series works
The A series follows one simple idea: each size is half of the one before it. Fold an A3 sheet in half across its long side and you get A4. Fold A4 in half and you get A5. The shape stays the same every time.
This works because the long side is about 1.414 times the short side (the square root of 2). When you cut a sheet with that shape in half, each half has the same shape again. Letter paper does not do this. Its ratio is 1.294, so half a Letter sheet is a different shape.
The biggest size, A0, measures 841 × 1,189 mm. That is almost exactly 1 square metre (0.9999 m²). So A1 is half a square metre, A2 a quarter, and so on. Each time you halve the long side, any part of a millimetre is dropped. That is why A5 is 148 mm wide and not 148.5 mm.
A-series paper size chart (A0 to A10)
| Size | Millimetres | Centimetres | Inches | Common use |
|---|---|---|---|---|
| A0 | 841 × 1189 | 84.1 × 118.9 | 33.1 × 46.8 | Technical drawings, large posters |
| A1 | 594 × 841 | 59.4 × 84.1 | 23.4 × 33.1 | Posters, plans |
| A2 | 420 × 594 | 42 × 59.4 | 16.5 × 23.4 | Posters, flip charts |
| A3 | 297 × 420 | 29.7 × 42 | 11.7 × 16.5 | Charts, drawings, small posters |
| A4 | 210 × 297 | 21 × 29.7 | 8.3 × 11.7 | Letters, forms, printing |
| A5 | 148 × 210 | 14.8 × 21 | 5.8 × 8.3 | Notebooks, flyers |
| A6 | 105 × 148 | 10.5 × 14.8 | 4.1 × 5.8 | Postcards, pocket notebooks |
| A7 | 74 × 105 | 7.4 × 10.5 | 2.9 × 4.1 | Small notes, labels |
| A8 | 52 × 74 | 5.2 × 7.4 | 2.0 × 2.9 | Small cards |
| A9 | 37 × 52 | 3.7 × 5.2 | 1.5 × 2.0 | Tiny labels |
| A10 | 26 × 37 | 2.6 × 3.7 | 1.0 × 1.5 | Stamps, tiny labels |
What about B sizes?
ISO 216 also sets a B series. B sizes sit between the A sizes, so B4 is between A3 and A4. B0 is 1,000 × 1,414 mm, B4 is 250 × 353 mm and B5 is 176 × 250 mm. B sizes are often used for books, posters and envelopes.
Watch out for Japanese B sizes. Japan’s JIS B series is slightly larger than the ISO one. JIS B5 is 182 × 257 mm, while ISO B5 is 176 × 250 mm. The W3C’s CSS page-size rules list both as separate sizes, so a “B5” notebook from Japan may not match a “B5” from elsewhere.
North American paper sizes: Letter, Legal and Tabloid
North American sizes are measured in inches. They do not halve neatly like the A series, so they have different shapes.
| Size | Inches | Millimetres | Closest ISO size |
|---|---|---|---|
| Letter | 8.5 × 11 | 215.9 × 279.4 | A4 (210 × 297) |
| Legal | 8.5 × 14 | 215.9 × 355.6 | None (longer than A4) |
| Ledger / Tabloid | 11 × 17 | 279.4 × 431.8 | A3 (297 × 420) |
Letter is written into official rules. For example, the US Securities and Exchange Commission’s filing rule (17 CFR 260.7a-17) says papers must be no larger than 8½ × 11 inches. In Canada, the federal government’s stationery rules set letterhead at Letter size, 216 × 279 mm (8.5 × 11 in), and Legal at 216 × 356 mm (8.5 × 14 in).
Which countries use A4 and which use Letter?
A4 and the other ISO 216 sizes are the everyday sizes in most countries. Letter is the everyday size in the United States and Canada. If you are not sure which one a country uses, check the paper sold in local shops or the default setting on a local printer.
Canada is an interesting case. It is a metric country, yet its federal stationery rules use Letter and Legal, as shown above. They simply write the inch sizes in rounded millimetres (216 × 279 mm).
Printing A4 on Letter paper (and Letter on A4)
Because the sizes are close, most files print fine on either paper if you let the printer scale them a little. Here is what to do.
- Set the document size first. In Word, Google Docs or any design app, choose A4 or Letter before you start typing. Changing it later can move page breaks.
- A4 file on Letter paper: the bottom of an A4 page will not fit. Choose “Fit to page” or “Scale to fit” in the print box. The text gets about 6% smaller.
- Letter file on A4 paper: the page is about 6 mm too wide. Choose “Fit to page” again. This time the text only gets about 3% smaller.
- Sending files abroad? Save as PDF. The reader can then print on their local paper with “Fit to page”.
Paper size also changes how many words fit on a page. Our test of how many pages 1,000 words takes found slightly fewer pages on A4 than on Letter with the same font and margins. If you send invoices to clients in other countries, see what to include on an invoice, and use a PDF so the layout stays the same.
Is ISO 216 still the current standard?
Yes. The current edition is ISO 216:2007 (edition 2). ISO’s own page says it was last reviewed and confirmed in 2021, so it remains current. ISO reviews every standard every five years, and it lists ISO 216 as under review again now. The A4 and Letter sizes are very well established, so a review is very unlikely to change them.
The A series is built on the metre, which is why its sizes are given in millimetres. For a quick refresher on how milli, centi and kilo work, read our guide to metric prefixes.
Frequently asked questions
What size is A4 in inches?
A4 is 8.27 × 11.69 inches, often rounded to 8.3 × 11.7 inches. In millimetres it is 210 × 297 mm.
What size is A4 in cm?
A4 is 21 × 29.7 cm.
Is Letter size the same as A4?
No. Letter is 8.5 × 11 inches (215.9 × 279.4 mm). A4 is 210 × 297 mm. Letter is about 6 mm wider and about 18 mm shorter than A4.
Which is bigger, A4 or Letter?
A4 is taller and has about 3% more area. Letter is wider. So A4 is slightly bigger overall, but neither sheet fits fully inside the other.
What is the difference between Letter, Legal and Tabloid?
Letter is 8.5 × 11 in. Legal is the same width but longer, at 8.5 × 14 in. Tabloid (also called Ledger) is 11 × 17 in, which is two Letter sheets side by side.
How many A4 sheets make an A3?
Two. A3 (297 × 420 mm) is exactly two A4 sheets side by side. In the same way, two A5 sheets make one A4.
Why is A4 such an odd size?
Because it starts from A0, which is 1 square metre with a long side about 1.414 times the short side. A4 is A0 halved four times, which gives 210 × 297 mm.
Can I print an A4 document on Letter paper?
Yes. Choose “Fit to page” or “Scale to fit” in your print settings. The page shrinks by about 6% so nothing is cut off at the bottom.
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