How cm, DPI and pixels fit together
A digital image has pixels, not centimetres. The DPI (dots per inch) says how many pixels go into one inch when it is printed, so pixels = size in cm ÷ 2.54 × DPI. A 3.5 cm wide photo at 300 DPI is 3.5 ÷ 2.54 × 300 ≈ 413 pixels wide. Kilomill does this sum for you, resizes to those pixels and writes the DPI into JPG, TIFF and PDF files.
| Print size | Common use | 200 DPI | 300 DPI | 600 DPI | |
|---|---|---|---|---|---|
| 3.5 × 4.5 cm | Passport-style photo on many forms | 276 × 354 px | 413 × 531 px | 827 × 1063 px | Use |
| 2.5 × 3.5 cm | PAN application photo (Protean, 200 DPI) | 197 × 276 px | 295 × 413 px | 591 × 827 px | Use |
| 2 × 2.5 cm | Stamp-size photo | 157 × 197 px | 236 × 295 px | 472 × 591 px | Use |
| 4.5 × 2 cm | PAN application signature (Protean, 200 DPI) | 354 × 157 px | 531 × 236 px | 1063 × 472 px | Use |
| 2 × 2 in (5.08 cm) | Square photo, e.g. US passport print | 400 × 400 px | 600 × 600 px | 1200 × 1200 px | Use |
| 4 × 6 in (10.2 × 15.2 cm) | Standard photo print | 800 × 1200 px | 1200 × 1800 px | 2400 × 3600 px | Use |
| 21 × 29.7 cm (A4) | Full page document | 1654 × 2339 px | 2480 × 3508 px | 4961 × 7016 px | Use |
Pixel values are width × height, rounded to the nearest pixel. PAN sizes from Protean’s online application instructions, read 28 October 2026. Always check the size your form or printer asks for.
Which DPI should I choose?
- 200 DPI: what many online forms ask for (for example the PAN application). Small files.
- 300 DPI: the usual print quality for photos and documents.
- 600 DPI: fine detail such as signatures or line art to be printed small; larger files.
If a form gives a size in cm and a file limit in KB but no DPI, start with 200 DPI: it reaches small KB limits more easily. Set File size → Target size for the KB limit in the same pass.
When the shape does not match
A phone photo is 3:4 and a 3.5 × 4.5 cm photo is 7:9, so something has to give. Fill exactly (crop the edges) fills the size and trims a little from the sides; Fill exactly (add a border) keeps the whole picture and adds a plain border; Fit inside keeps the shape and makes one side smaller than asked. Use Crop first to choose exactly what stays.
Updated