How print size is worked out
A print has no pixels of its own: the pixels of the photo are spread over the paper. How many of them land on each inch decides how sharp the print looks. That number is the resolution of the print, in pixels per inch (ppi). Divide the pixels of the photo by the resolution and you get the size in inches; multiply by 2.54 for centimetres. A photo 4032 px wide printed at 300 ppi is 13.4 in, or 34.1 cm, wide.
Pixels you need for common print sizes
| Best, 300 ppi | From a distance, 150 ppi | |
|---|---|---|
| 10 × 15 cm (4 × 6 in) | 1181 × 1772 px (1200 × 1800 px) | 591 × 886 px (600 × 900 px) |
| 13 × 18 cm (5 × 7 in) | 1535 × 2126 px (1500 × 2100 px) | 768 × 1063 px (750 × 1050 px) |
| A4 (21 × 29.7 cm) | 2480 × 3508 px | 1240 × 1754 px |
| 8 × 10 in | 2400 × 3000 px | 1200 × 1500 px |
| A3 (29.7 × 42 cm) | 3508 × 4961 px | 1754 × 2480 px |
| 16 × 20 in | 4800 × 6000 px | 2400 × 3000 px |
What resolution do you need?
300 ppi is the standard for photo prints that are held in the hand, such as photos in an album, cards and small frames: at that resolution the eye sees no pixels even up close. 200 ppi still looks sharp at arm’s length and suits most prints on a desk or a shelf. 150 ppi is enough for large prints on a wall, which people look at from a step or two away. Below that, edges start to look soft.
DPI, PPI and the 72 dpi myth
People often say dpi, dots per inch, when they mean ppi. Strictly, dpi is about the printer: how many dots of ink it lays down. For working out a print size, what matters is how many pixels of the photo land on an inch. The dpi value stored in a file, often 72, changes nothing: a photo of 4032 × 3024 px has the same pixels whatever number is written in it, and prints at the same size and quality.
When the photo and the print have different shapes
Most cameras take photos at 3:2 and most phones at 4:3, while prints come in many shapes: 10 × 15 cm is 3:2, 8 × 10 in is 4:5, A4 is close to 7:10. When the shapes differ, the photo is cropped to fill the print, and the table shows how much is cut off. Crop the photo yourself before ordering, so that you choose what is lost.
Can you print bigger than this?
You can, but the print gets softer. Making a photo larger in software adds pixels, not detail. For a big print that will hang on a wall, 150 ppi is usually fine; for something people will hold, stay close to 300 ppi.