How to convert cm, mm and inches to pixels
The formula for converting centimetres, millimetres and inches to pixels at any DPI, with a table of common sizes at 72, 96, 150 and 300 DPI.
You need a DPI
Centimetres measure paper and pixels measure a screen image, so you can’t convert between them without a DPI (dots per inch). The DPI says how many pixels go into one inch. If your form gives a size in cm but no DPI, look again in the instructions; 300 is common for print-style photos, but your form decides.
The formula
Pixels = inches × DPI. For millimetres, pixels = mm ÷ 25.4 × DPI. For centimetres, pixels = cm ÷ 2.54 × DPI. Round to the nearest whole pixel.
1 cm and 1 inch
1 cm is 28 px at 72 DPI, 38 px at 96 DPI, 59 px at 150 DPI and 118 px at 300 DPI. 1 inch is simply the DPI: 72, 96, 150 or 300 px.
3.5 × 4.5 cm (35 × 45 mm)
At 72 DPI this is 99 × 128 px, at 96 DPI 132 × 170 px, at 150 DPI 207 × 266 px, and at 300 DPI 413 × 531 px.
2 × 2 inches
At 72 DPI this is 144 × 144 px, at 96 DPI 192 × 192 px, at 150 DPI 300 × 300 px, and at 300 DPI 600 × 600 px.
4 × 6 inches and A4
A 4 × 6 inch print is 288 × 432 px at 72 DPI, 384 × 576 px at 96 DPI, 600 × 900 px at 150 DPI and 1200 × 1800 px at 300 DPI. An A4 page (210 × 297 mm) is 595 × 842 px at 72 DPI, 794 × 1123 px at 96 DPI, 1240 × 1754 px at 150 DPI and 2480 × 3508 px at 300 DPI.
Converting in the tool
You don’t have to calculate by hand. Use /cm-to-pixels/, /mm-to-pixels/ or /inch-to-pixels/ for a quick answer, or choose cm, mm or inch directly in the resizer and enter the DPI. The tool computes the pixels the same way and writes the DPI into the JPEG file.
Questions
How many pixels is 1 cm?
It depends on the DPI: 1 cm is 28 px at 72 DPI, 38 px at 96 DPI and 118 px at 300 DPI. The formula is cm ÷ 2.54 × DPI.
What is 3.5 × 4.5 cm in pixels?
3.5 × 4.5 cm is 413 × 531 px at 300 DPI, 276 × 354 px at 200 DPI and 132 × 170 px at 96 DPI.
What DPI should I use to convert cm to pixels?
Use the DPI your form or printer states. If none is given, 300 DPI is a common choice for photos that may be printed, and 96 DPI matches the usual screen measurement on Windows.
Updated 2026-11-06