When you need this conversion
US and UK print work is often specified in inches: 4 × 6 photo prints, 8.5 × 11 Letter pages, 24 × 36 posters. If you have an image and want to know which of those sizes it can fill sharply, divide its pixel dimensions by the print DPI.
What size can I print?
Take the pixel width and height and divide each by 300:
- 2400 × 3000 px prints at 8 × 10 in.
- 1800 × 1200 px prints at 6 × 4 in, a standard photo.
- 4000 × 3000 px (a 12 MP camera) prints at 13.3 × 10 in.
Posters can go lower. At 150 DPI the same 4000 px image prints 26.7 inches wide, which looks fine from a meter away.
In CSS
Browsers define 1in as exactly 96px. So width: 1in is always 96 CSS pixels, whatever the screen. On paper (when printing a web page) that inch is real; on screen it is only approximately an inch.
Common mistakes
Believing the file’s DPI setting. The DPI stored in a JPEG is only a label. Changing it from 72 to 300 without resampling changes the printed size, not the detail.
Enlarging past the pixels. If an image comes out at 4 inches at 300 DPI and you need 8, printing it at 8 inches means 150 DPI. That can be fine for a poster, but it will look soft in a photo book.
Reverse it with the inches to pixels converter, or check both dimensions at once with the image print size calculator.