Converting centimetres to pixels
Photo specifications are published in physical units because they were written for print, while uploads need pixels. The conversion depends entirely on DPI — dots per inch — and there is no single right answer without it.
The formula is: pixels = (mm ÷ 25.4) × DPI. So 35mm at 300 DPI gives (35 ÷ 25.4) × 300 = 413 pixels, and 45mm gives 531. At 600 DPI you would get 827 × 1063.
| DPI | Pixel size | Typical use |
|---|---|---|
| 150 DPI | 207 × 266 px | Screen only — too low for print |
| 300 DPI | 413 × 531 px | Standard print requirement |
| 600 DPI | 827 × 1063 px | High-quality print, some embassies |
Which countries use 3.5 × 4.5 cm
The UK, all Schengen countries, Australia, New Zealand, Japan, South Korea, Singapore, Malaysia, Thailand, Turkey, South Africa, Brazil and most of the rest of Europe and Asia.
The main exceptions are the United States, India and Canada. The US and India use 2 × 2 inch squares; Canada uses 50 × 70mm, which is larger and a different ratio.
Frequently asked questions
- How many pixels is 3.5 x 4.5 cm?
- 413 × 531 pixels at 300 DPI, which is the standard print requirement. At 600 DPI it is 827 × 1063.
- Is 3.5 x 4.5 cm the same as 35 x 45 mm?
- Yes, identical — 1 cm is 10mm. Specifications are written both ways.
- What DPI should I use?
- 300 DPI unless your authority says otherwise. It is the near-universal minimum for print. Only use 600 if it is specifically required, and only if your source photo genuinely has that much detail.