How do I convert cm to pixels?
Pixels depend on resolution (DPI, dots per inch). Divide the size in cm by 2.54 to get inches, then multiply by the DPI: pixels = cm ÷ 2.54 × DPI. A 3.5 cm wide passport photo at 300 DPI is 3.5 ÷ 2.54 × 300 = 413 pixels. FixDoks's CM to Pixels converter does this for cm, mm and inches, and also converts pixels back to cm.
CM to Pixels at a glance
| Units | cm, mm, inches, pixels |
|---|---|
| DPI | 72, 96, 150, 200, 300, 600 or any custom value |
| Formula | pixels = cm ÷ 2.54 × DPI |
| Processing | In your browser; your files are not uploaded |
| Price | Free |
| Works on | Chrome, Edge, Safari and Firefox on Windows, Mac, Android and iPhone |
How to use CM to Pixels Converter
- Tap a preset such as Passport photo 3.5 × 4.5 cm, or enter your own width and height.
- Choose the unit (cm, mm or inches) and the DPI: 300 is standard for print, 200 is used by many Indian forms.
- Read the size in pixels, with the same size at other DPI values in the table.
- To go the other way, switch to Pixels to size and enter the width and height in pixels.
Why cm to pixels needs a DPI
A centimetre is a physical length, but a pixel has no fixed size. How many pixels fit in a centimetre depends on the resolution, measured in DPI (dots per inch) or PPI (pixels per inch). At 300 DPI, one inch of print holds 300 pixels; at 72 DPI it holds only 72. So the same 3.5 cm photo can be 99 pixels wide or 827 pixels wide, depending on the DPI you choose.
The formulas
- cm to pixels: pixels = cm ÷ 2.54 × DPI
- mm to pixels: pixels = mm ÷ 25.4 × DPI
- inches to pixels: pixels = inches × DPI
- pixels to cm: cm = pixels ÷ DPI × 2.54
One inch is exactly 2.54 cm, so these conversions are exact. The only rounding is to whole pixels at the end, because an image cannot have part of a pixel.
Common photo and signature sizes
| Size | DPI | Pixels |
|---|---|---|
| Passport photo 3.5 × 4.5 cm | 300 | 413 × 531 px |
| Passport photo 3.5 × 4.5 cm | 200 | 276 × 354 px |
| US photo 2 × 2 inch (51 × 51 mm) | 300 | 600 × 600 px |
| Signature 6 × 2 cm (SSC style) | 200 | 472 × 157 px |
| Signature 4.5 × 2 cm (PAN, Protean) | 200 | 354 × 157 px |
These are the same figures our form tools use. SSC asks for a signature of about 6.0 × 2.0 cm and gives no pixel size; at 200 DPI that is 472 × 157 pixels, which is what the SSC photo and signature resizer makes. Forms also set a file size limit in KB, which depends on the image content, not just the pixel count, so always check the current notification for your form.
Which DPI should I use?
| DPI | Typical use |
|---|---|
| 72 and 96 | Screen layouts. 96 is the CSS reference: one CSS inch is 96 px. |
| 150 | Draft prints and documents where file size matters |
| 200 | Many Indian application forms and scanned documents |
| 300 | Standard photo and print quality |
| 600 | High quality scans of signatures, line art and small text |
From pixels to a print size
Switch to Pixels to size to see how large an image will print. A 1200 × 1800 px photo prints at 10.16 × 15.24 cm (a 4 × 6 inch print) at 300 DPI, or twice that size at 150 DPI with less detail. If an upload form asks for a size in cm, work out the pixels here first, then make the file with the image resizer.
Next steps
- Make a passport photo at the right size with the passport size photo maker.
- Resize any photo to exact pixels with Resize Image.
- Exam forms: use the ready made tools for SSC, IBPS, UPSC and PAN card photos and signatures, which also handle the KB limits.