Print Size Cheat Sheet: How Many Pixels You Need for A4, A3 and Posters
300 DPI, 200 DPI, pixel counts for A5 to A1 and 10×15 prints — plus why the old "72 DPI images cannot be printed" rule is wrong and pixels are all that matter.
Every print question reduces to one number: how many pixels do I have, and how big will that be on paper. DPI is just that division with a target attached. Here are the numbers, then the parts people get wrong.
The table
Pixels needed to print each size at 300 DPI, the standard for anything viewed in hand, and at 200 DPI, which is fine for posters and large prints seen from a distance.
| Print size | At 300 DPI | At 200 DPI |
|---|---|---|
| 10×15 cm (6×4 in) | 1181×1772 | 787×1181 |
| A5 (14.8×21 cm) | 1748×2480 | 1165×1654 |
| A4 (21×29.7 cm) | 2480×3508 | 1654×2339 |
| A3 (29.7×42 cm) | 3508×4961 | 2339×3307 |
| A2 (42×59.4 cm) | 4961×7016 | 3307×4677 |
| A1 (59.4×84.1 cm) | 7016×9933 | 4677×6622 |
| 50×70 cm poster | 5906×8268 | 3937×5512 |
Reading the table backwards
If you have a 1200×1600 phone photo, it prints 10×15 cm at about 270 DPI, and A4 at about 150 DPI. That last number is the useful one: divide your pixels by the centimetres and multiply by 2.54 to get the DPI you will actually get.
To go bigger you have two levers: upscale the file, or drop the DPI. A poster on a wall is viewed from a metre away, so 150–200 DPI is invisible to the eye, and doubling the physical size instead of the pixel count is often the smarter trade. Our factor guide covers how to pick the multiplier once you know the target.
Three things people get wrong
“72 DPI images cannot be printed.” DPI is not a property of an image file; it is a property of the print. A 3000-pixel-wide image printed 100 cm wide is 76 DPI and that is fine at that size. The only real question is pixel dimensions.
“More DPI is always better.” Above roughly 300 DPI on paper you are paying for pixels the eye cannot resolve at reading distance, and most print services resample to 300 DPI anyway. For posters, 150–200 DPI is a normal, professional choice.
“Upscaling adds printable detail.” It adds pixels, and the printer will use them. It does not add information — a soft 800-pixel photo printed A4 after 4x upscaling still looks like a soft photo, just a smoother one. That is often good enough, and it is a different claim from “more detail”.
Preparing a file for print
- Compute the target pixels from the table, using the size you will actually hang or hand over.
- Compare with your source: if the factor is 2x or 4x, a normal upscale is a reasonable step. If it is 8x or higher, consider a smaller print first.
- Keep the aspect ratio. Cropping after an upscale is normal, stretching is not.
- Sharpen at the very end, at the final resolution, and lightly. Printers and their own resampling will do some of the work.
- Ask the print service what DPI they expect. Poster shops usually ask for 150–200 DPI files, not 300.
Upload limits, for reference
Free accounts on Bigjpg take files up to 3000×3000 pixels and 5 MB, which comfortably covers A4 at 300 DPI. Paid accounts go to 50 MB per image (plans), which is what you need for A3 and A2 sources. Uploaded files are deleted automatically — 24 hours on free accounts, 72 on paid.
Check a file before you send it anywhere: enlarge an image free up to 3000×3000 pixels without an account, then compare the result with the original at 100 % before you order the print.