If you have ever wondered why a passport photo is described as both "35 x 45 mm" and "413 x 531 pixels", this guide explains the relationship between physical size, pixels and DPI — and why the numbers your online application asks for may not match the printed size at all.
DPI links millimetres to pixels
DPI (dots per inch) is how many pixels fit into one inch of print. Passport photos are almost always printed at 300 DPI, the standard for sharp photographic prints.
The formula is simple:
pixels = (millimetres ÷ 25.4) × DPI
So a 35 x 45 mm photo at 300 DPI is:
- width: (35 ÷ 25.4) × 300 ≈ 413 px
- height: (45 ÷ 25.4) × 300 ≈ 531 px
Common sizes at 300 DPI
| Physical size | Pixels @ 300 DPI |
|---|---|
| 2 x 2 in (US, India) | 600 x 600 |
| 35 x 45 mm (UK, EU, Japan) | 413 x 531 |
| 50 x 70 mm (Canada) | 591 x 827 |
| 33 x 48 mm (China) | 390 x 567 |
Note that 2 x 2 inches is exactly 600 x 600 px at 300 DPI. You may see 602 x 602 quoted if someone rounds 51 mm — but 2 inches is 50.8 mm, which gives a clean 600.
Printed size vs digital application size
Here is the trap: many countries publish a separate pixel specification for online applications that is not the same as the printed size.
- The UK digital photo, for example, must be at least 600 x 750 px with a file between 50 KB and 10 MB — and the system crops it for you, so you should not crop it yourself.
- Printed UK photos, by contrast, are 45 x 35 mm (about 531 x 413 px at 300 DPI).
So "413 x 531 px" is right for a printed UK photo but wrong for the UK digital service. Always check which channel — paper or online — you are using.
File-size and format tips
- Online systems usually accept JPEG and set a maximum file size (often a few MB) and sometimes a minimum (to reject low-quality images).
- Don't over-compress: heavy JPEG compression creates blocky artefacts that can fail automated checks.
- Keep the aspect ratio correct — stretching to hit a pixel target distorts the face.
Get the numbers right automatically
GetShot Passport sizes your photo to the correct pixels and 300 DPI for your chosen country and channel, and exports a print-ready file — in your browser, without uploading. It won't stretch or distort the image to hit a target.
FAQ
What DPI should a passport photo be? 300 DPI for printing. Digital-only submissions are specified in pixels instead.
Is 2 x 2 inches 600 or 602 pixels? 600 x 600 at 300 DPI. Two inches is exactly 50.8 mm; quoting 51 mm gives a misleading 602.
Why does my online application want a different pixel size than the printed one? Because many authorities publish a separate digital spec (e.g. the UK's 600 x 750 px minimum) that differs from the printed size. Use the spec for your submission channel.