CM to Pixels Converter: the 300 DPI Calculator
Updated · PixKB
Forms often give a photo size in centimetres: "3.5 × 4.5 cm", "minimum 4.5 cm high". A digital photo is measured in pixels, and the bridge between the two is the resolution, in dots (pixels) per inch: DPI. Pick the wrong DPI and a photo of the right shape can have far too few pixels for the form.
Enter a size and DPI; the pixel result updates as you type. Everything runs in your browser.
3.5 × 4.5 cm at 300 DPI
Need the photo itself resized? Resize an image in cm, mm or inches: the same maths, applied to your file, with the DPI saved in it.
The formula
Pixels = centimetres ÷ 2.54 × DPI (or millimetres ÷ 25.4 × DPI, or inches × DPI). So 3.5 × 4.5 cm is 413 × 531 pixels at 300 DPI, 276 × 354 at 200 DPI and 132 × 170 at 96 DPI: the same physical size, very different files.
Which DPI to use
If the form states a DPI, use it. If it states only centimetres, 300 DPI is the safe choice: it's the usual print resolution for photos, so the file has enough pixels to print sharply at that size, and a portal that checks pixels gets a generous number. If the form states pixels, the pixels are what's checked, whatever the cm figure.
DPI in the file vs pixels in the photo
A photo's DPI setting is only a note saying how big to print it; changing that number alone doesn't change a single pixel. What changes the photo is resizing it to the pixel count. PixKB's cm resizer does both: it resizes to the pixels and records the DPI in the JPEG, so Word and print dialogs show the intended size when printing at actual size (100%).
Common sizes
3.5 × 4.5 cm and 35 × 45 mm are the same size: 413 × 531 pixels at 300 DPI. 2 × 2 inches (5.08 cm) is 600 × 600 pixels, the US visa minimum. A 6 × 2 cm signature box is 709 × 236 pixels. An ID card (86 × 54 mm) is 1016 × 638 pixels, landscape.
Lookup table: 300, 200, 150 and 96 DPI
| Size | Used for | 300 DPI | 200 DPI | 150 DPI | 96 DPI |
|---|---|---|---|---|---|
| 3.5 × 4.5 cm | PPSC photo (minimum); other forms that state 3.5 × 4.5 cm | 413 × 531 | 276 × 354 | 207 × 266 | 132 × 170 |
| 35 × 45 mm | India passport photo (same size in mm) | 413 × 531 | 276 × 354 | 207 × 266 | 132 × 170 |
| 6 × 2 cm | SSC signature | 709 × 236 | 472 × 157 | 354 × 118 | 227 × 76 |
| 5.08 × 5.08 cm (2 × 2 in) | US visa and DV lottery photo | 600 × 600 | 400 × 400 | 300 × 300 | 192 × 192 |
| 8.6 × 5.4 cm | ID card such as Pakistan's CNIC (PPSC CNIC picture), landscape | 1016 × 638 | 677 × 425 | 508 × 319 | 325 × 204 |
| 21 × 29.7 cm | A4 page | 2480 × 3508 | 1654 × 2339 | 1240 × 1754 | 794 × 1123 |
Pixels = cm ÷ 2.54 × DPI, rounded to the nearest pixel. If a portal states pixels, use its figure: it overrides any cm conversion.
The resizer applies these numbers to your photo and shows the pixel result before you resize, so you don't need to do the arithmetic.
Frequently asked questions
How many pixels is 3.5 × 4.5 cm at 300 DPI?
413 × 531 pixels: 3.5 ÷ 2.54 × 300 = 413 and 4.5 ÷ 2.54 × 300 = 531.
What is 300 DPI in pixels per centimetre?
About 118 pixels per cm (300 ÷ 2.54), or 11.8 per mm. Multiply by your size.
What DPI should I use if the form doesn't say?
300 DPI, the usual print resolution for photos. If the form gives pixels, use those instead: they are what's checked.
Does DPI change the file size in KB?
Indirectly. A higher DPI means more pixels for the same physical size, and more pixels usually means more KB.
Is 35 × 45 mm the same as 3.5 × 4.5 cm?
Yes. Both are 413 × 531 pixels at 300 DPI.
Does changing the DPI number alone change the photo?
No. A photo's DPI setting only says how big to print it. Only changing the pixel size changes the photo. PixKB's resizer does both: it resizes to the pixels and saves the DPI.
How many pixels is an ID card (86 × 54 mm)?
1016 × 638 pixels at 300 DPI, landscape.