Pixels, resolution, DPI: sizing a photo for print
A screen only has pixels; DPI only means something on paper. One formula and one table cover every size you will meet.
Updated 2026-09-10
A digital photo has no size, only a pixel count. A 4032x3024 photo is 4032 dots across and 3024 down, and how many centimetres that is has not been decided. The centimetres are decided by how densely those dots are placed on paper. That density is DPI.
There is one formula
Pixels = inches × DPI. Starting from centimetres, divide by 2.54 to get inches, then multiply. The print standard is 300dpi: 300 dots per inch is dense enough that the eye cannot separate them, so it reads as a photograph. A 10x15cm print at 300dpi needs (10÷2.54×300) by (15÷2.54×300), which is 1181x1772 pixels.
| Print size | Pixels at 300dpi | Pixels at 150dpi |
|---|---|---|
| ID photo 3 x 4 cm | 354 x 472 | — |
| Business card 9 x 5 cm | 1063 x 591 | — |
| 4 x 6 in (10 x 15 cm) | 1200 x 1800 | 600 x 900 |
| 5 x 7 in (13 x 18 cm) | 1500 x 2100 | 750 x 1050 |
| 8 x 10 in (20 x 25 cm) | 2400 x 3000 | 1200 x 1500 |
| A5 (148 x 210 mm) | 1748 x 2480 | 874 x 1240 |
| A4 (210 x 297 mm) | 2480 x 3508 | 1240 x 1754 |
| A3 (297 x 420 mm) | 3508 x 4961 | 1754 x 2480 |
| A2 (420 x 594 mm) | 4961 x 7016 | 2480 x 3508 |
When 300 is more than you need
300dpi is for prints held in the hand. A poster on a wall or a banner is viewed from further away, so 150dpi is fine and a large banner works at 72. Double the viewing distance and the DPI you need halves. The reverse holds too: an ID photo examined up close needs the full 300.
A typical phone photo is 12 megapixels, which is 4032x3024. That covers a 4x6 at 300dpi with room to spare, and A4 at 300dpi too. A3 wants 4961 on the long side and the phone has 4032, so it falls a little short — but printed at 244dpi it is fine on a wall. Do not scale up to make the numbers work. Scaling invents pixels; it does not create sharpness.
Changing the DPI number changes nothing
Some image files carry a DPI value as metadata. Changing it from 72 to 300 adds not one pixel. It is only a hint that print software uses to work out the size on paper. When a print shop asks for a 300dpi file, they are not asking for that number; they are asking for enough pixels to print the size you want at 300dpi.
The idea that screen images should be 72dpi is the same misunderstanding. A screen ignores DPI and looks only at pixels. A 1080-pixel image is 1080 pixels on screen whatever the DPI field says.
Handing a file to a print shop
- Ask about bleed. Most shops want 3mm on every side. For A4 that is 216x303mm, or 2551x3579 pixels at 300dpi.
- Fill the bleed with background, and keep anything important at least 3mm inside the trim line.
- Deliver PNG or maximum-quality JPG. The shop should never need to compress it again.
- If colour matters, expect print to differ from screen. Screens are light; paper is ink. Saturated blues and greens dull the most.