Size & print
DPI, PPI and pixels: what print size really means
How pixels become centimetres and inches on paper, and why 300 PPI is the usual number.
Pixels are all a digital image has
A digital photo is just a grid of pixels, like 4000 × 3000. It has no physical size until you decide how many pixels to place in each inch of paper.
PPI turns pixels into inches
Pixels per inch (PPI) sets that density: inches = pixels ÷ PPI. At 300 PPI, a 600-pixel-wide image prints 2 inches wide. People often say DPI, which strictly describes printer ink dots, but the idea is the same.
Why 300 PPI?
At normal viewing distance, 300 PPI looks sharp to most people, so it is the usual target for photo prints. Posters seen from further away can use less.
Working out pixels for a print
Convert millimetres to inches by dividing by 25.4, then multiply by the PPI. A 35 mm wide passport photo at 300 PPI needs 35 ÷ 25.4 × 300 ≈ 413 pixels.
Frequently asked questions
Does changing DPI change the image quality?
No. Changing only the DPI number in a file doesn’t add or remove pixels; it changes how large the image would print.
Passport & visa photos
Passport size photo maker
Choose a country and document to set the photo size, pixels and file limit, then crop. Free, and your image never leaves your browser.
Open Passport size photo maker