"How many pixels is A4?" has no single answer, and that is the source of endless confusion. A physical page has a physical size; pixels only acquire a physical size once you decide how many of them fit in an inch. This page gives the numbers for every common combination, and explains the system well enough that you can work out any size that is not listed.
The number you probably want
A4 at 300 DPI is 2480 × 3508 pixels. US Letter at 300 DPI is 2550 × 3300 pixels. Those two cover most print work. If you are designing for screen rather than print, use 96 DPI: A4 becomes 794 × 1123 and Letter becomes 816 × 1056.
Why the A series is designed the way it is
The ISO 216 A series is one of the more elegant pieces of standardisation in daily life, and understanding it takes about ninety seconds.
Start with two rules. First, A0 has an area of exactly one square metre. Second, the ratio of long side to short side is √2 (approximately 1.41421). Everything else follows.
The √2 ratio has a unique property: fold a √2 rectangle in half across its long edge and you get another √2 rectangle. No other ratio does this. Halve a 3:2 rectangle and you get 3:4 — a different shape. Halve a √2 rectangle and the proportions are identical.
The practical payoff is enormous. Photocopying A4 onto A3 is a clean 141% enlargement with no cropping and no leftover margin. Two A5 sheets fill an A4 exactly. A booklet folds without a single measurement being recalculated. Compare this to US Letter, which has no such relationship to any other American size — enlarging Letter to Tabloid always leaves a margin, because their aspect ratios differ.
Solving the two rules gives A0 = 841 × 1189 mm. That is an area of 999,949 mm², one square metre to within a rounding error — the sides are rounded down to whole millimetres, which is where the missing 51 mm² goes.
💡 The B and C series
Two companion series exist for the same reason. B sizes sit geometrically between two A sizes and are used for posters and books where A feels wrong. C sizes are for envelopes: a C4 envelope holds an unfolded A4 sheet, a C5 holds A4 folded once, and a C6 holds A4 folded twice. That is why a standard business envelope is a DL or C5 — the naming encodes exactly what fits inside.
The A series in millimetres
| Size | Millimetres | Inches | Typical use |
|---|---|---|---|
| A0 | 841 × 1189 | 33.11 × 46.81 | Technical drawings, large posters |
| A1 | 594 × 841 | 23.39 × 33.11 | Posters, flip charts |
| A2 | 420 × 594 | 16.54 × 23.39 | Posters, art prints |
| A3 | 297 × 420 | 11.69 × 16.54 | Spreadsheets, small posters, menus |
| A4 | 210 × 297 | 8.27 × 11.69 | The default document size worldwide |
| A5 | 148 × 210 | 5.83 × 8.27 | Notebooks, flyers, paperbacks |
| A6 | 105 × 148 | 4.13 × 5.83 | Postcards |
| A7 | 74 × 105 | 2.91 × 4.13 | Tickets, small cards |
| A8 | 52 × 74 | 2.05 × 2.91 | Business cards (some regions) |
The A series in pixels
The conversion is simply pixels = millimetres ÷ 25.4 × DPI. Here is every combination worked out, rounded to the nearest pixel.
At 300 DPI — standard print quality
| Size | Portrait (px) | Landscape (px) |
|---|---|---|
| A0 | 9933 × 14043 | 14043 × 9933 |
| A1 | 7016 × 9933 | 9933 × 7016 |
| A2 | 4961 × 7016 | 7016 × 4961 |
| A3 | 3508 × 4961 | 4961 × 3508 |
| A4 | 2480 × 3508 | 3508 × 2480 |
| A5 | 1748 × 2480 | 2480 × 1748 |
| A6 | 1240 × 1748 | 1748 × 1240 |
At other resolutions
| Size | 72 DPI | 96 DPI | 150 DPI | 600 DPI |
|---|---|---|---|---|
| A3 | 842 × 1191 | 1123 × 1587 | 1754 × 2480 | 7016 × 9921 |
| A4 | 595 × 842 | 794 × 1123 | 1240 × 1754 | 4961 × 7016 |
| A5 | 420 × 595 | 559 × 794 | 874 × 1240 | 3496 × 4961 |
| A6 | 298 × 420 | 397 × 559 | 620 × 874 | 2480 × 3496 |
⚠️ 595 × 842 is not a pixel size
A4 at 72 DPI comes out as 595 × 842, and you will see those numbers constantly in PDF work. They are not really pixels — they are PostScript points, and a point is defined as exactly 1/72 inch. PDF measures everything in points, which is why 595 × 842 is the internal size of every A4 PDF regardless of how sharp the images inside it are. Do not mistake this for a resolution limit.
North American sizes
The US, Canada, Mexico and the Philippines use a separate system with no mathematical relationship between sizes. The dimensions are historical rather than derived.
| Size | Inches | Millimetres | 96 DPI | 300 DPI |
|---|---|---|---|---|
| Letter | 8.5 × 11 | 216 × 279 | 816 × 1056 | 2550 × 3300 |
| Legal | 8.5 × 14 | 216 × 356 | 816 × 1344 | 2550 × 4200 |
| Tabloid / Ledger | 11 × 17 | 279 × 432 | 1056 × 1632 | 3300 × 5100 |
| Executive | 7.25 × 10.5 | 184 × 267 | 696 × 1008 | 2175 × 3150 |
| Half Letter | 5.5 × 8.5 | 140 × 216 | 528 × 816 | 1650 × 2550 |
The A4 / Letter mismatch
A4 is 6 mm narrower and 18 mm taller than Letter. That sounds trivial and causes real problems. A document laid out for A4 and printed on Letter loses 18 mm from the bottom — enough to orphan a footer or push a signature block onto its own page. Going the other way, a Letter layout on A4 leaves an uneven margin and shifts anything positioned from the bottom edge.
If a document will be printed on both continents, design inside the intersection: 210 mm wide (the A4 width) by 279 mm tall (the Letter height), which prints safely on either. Keep at least 15 mm of margin on all sides and nothing will be lost whichever paper is loaded.
Choosing the right DPI
More resolution is not automatically better. It is bounded by what the eye can resolve at the viewing distance, and beyond that point you are only making the file bigger.
| DPI | Use for | Viewing distance |
|---|---|---|
| 72–96 | Screen only, web mockups, email | Screen |
| 150 | Draft prints, internal documents, large posters | 1 m or more |
| 300 | Commercial print, brochures, photo books, magazines | ~30 cm |
| 600 | Fine line art, engraving, small type, archival scanning | Close inspection |
| 1200 | Specialist reproduction, halftone screening | Under magnification |
The rule of thumb professionals use: required DPI ≈ 300 ÷ viewing distance in feet. A poster viewed from 2 metres (about 6.5 feet) needs roughly 45 DPI to look perfectly sharp. Billboards are routinely produced at 10–20 DPI because nobody stands close enough to tell. Producing that same billboard at 300 DPI would create a file of tens of gigabytes to no visible benefit.
✅ How to check if an image is big enough to print
Divide the pixel dimensions by the target DPI to get the printable size in inches. A 3000 × 2000 photo at 300 DPI prints at 10 × 6.7 inches — roughly A4. The same file printed at A2 would be 100 DPI, which is fine for a wall poster and poor for a brochure. Work out the number before you send it to print, not after.
Bleed, trim and safe margins
Commercial printing does not print on a finished sheet; it prints on a larger sheet and cuts it down. Cutting is accurate to about a millimetre, so any artwork that ends exactly at the edge risks a white line where the blade drifted. Three regions matter:
- Bleed — artwork extended 3 mm beyond the finished size on every side. Backgrounds and edge-to-edge images must reach here.
- Trim — the finished size. Where the blade is aiming.
- Safe area — 5 mm inside the trim. All text and logos live here.
| Size | Trim (mm) | With 3 mm bleed | At 300 DPI with bleed |
|---|---|---|---|
| A3 | 297 × 420 | 303 × 426 | 3579 × 5031 |
| A4 | 210 × 297 | 216 × 303 | 2551 × 3579 |
| A5 | 148 × 210 | 154 × 216 | 1819 × 2551 |
| A6 | 105 × 148 | 111 × 154 | 1311 × 1819 |
A common mistake is to design at exactly A4 and then ask the printer to "add bleed". They cannot invent artwork that does not exist — the best they can do is scale your whole design up by about 3%, which shifts everything and softens the image. Set the bleed up at the start.
Paper sizes in CSS
Browsers can print to real paper sizes, and the CSS is simpler than most people expect:
CSS defines one inch as exactly 96 pixels, which is why 96 DPI appears in the tables above — it is the browser's fixed reference, regardless of your actual screen density. Physical units such as mm and cm are approximate on screen but accurate when printing, so a print stylesheet written in millimetres does what it says.
Need to resize an image to a print size?
Enter any of the pixel dimensions from this page and resize in your browser — the file never leaves your device.
Open the Image Resizer →Working it out yourself
Two formulas cover every case on this page:
A4 at 300 DPI: 210 ÷ 25.4 × 300 = 2480. That is the whole calculation. Once you internalise that a pixel dimension is meaningless without a DPI attached, and that DPI should be chosen from viewing distance rather than habit, the rest of print setup stops being mysterious.
Frequently Asked Questions
What size is A4 in pixels?
It depends entirely on the resolution. A4 is 210 × 297 mm, which is 2480 × 3508 pixels at 300 DPI (standard print), 1240 × 1754 at 150 DPI (draft print), 794 × 1123 at 96 DPI (CSS reference), and 595 × 842 at 72 DPI (classic PDF points). A pixel count with no DPI attached is meaningless for print.
Why is A4 that particular size?
A0 is defined as one square metre with sides in the ratio 1:√2. Every subsequent size is A0 folded in half across the long edge, which — because of the √2 ratio — preserves the aspect ratio exactly. A4 is A0 halved four times. The system means enlarging A4 to A3 or shrinking to A5 never leaves margins or requires cropping.
Is 300 DPI always necessary for printing?
No. 300 DPI is the standard for material viewed at reading distance, roughly 30 cm. Viewing distance is what matters: a poster read from two metres looks perfectly sharp at 150 DPI, and a billboard is often produced at 20 DPI or less. Printing everything at 300 DPI just creates huge files for no visible benefit.
What is the difference between A4 and US Letter?
A4 is 210 × 297 mm; Letter is 216 × 279 mm. Letter is about 6 mm wider and 18 mm shorter. They are close enough that documents mostly print on either, but not identical — an A4 layout printed on Letter loses about 18 mm at the bottom, which is exactly enough to push a footer onto a second page.
What is bleed and how much do I need?
Bleed is artwork extended beyond the trim line so that slight cutting inaccuracy never leaves a white sliver at the edge. Standard bleed is 3 mm on each side. An A4 document with bleed is set up at 216 × 303 mm, and anything critical should stay at least 5 mm inside the trim line.