Resize an Image in cm, mm or Inches
Enter a physical size and DPI — the tool calculates exact pixels. Presets for passport, PAN, signature and A4.
Resize an image in centimetres, millimetres or inches
Photo printing, passport forms and ID cards are specified in physical units, not pixels. A passport photo is 3.5 by 4.5 cm. A PAN card photograph is 2.5 by 3.5 cm. A signature strip is often 3.5 by 1.5 cm. Your phone camera only understands pixels, so at some point somebody has to convert one into the other. That conversion needs a third number: the print resolution, measured in dots per inch.
This tool does the arithmetic for you. Enter the width and height in your chosen unit, pick the DPI the printer or portal expects, and it calculates the exact pixel dimensions and resizes the image to match.
The formula, so you can check the result yourself
Pixels equal physical size divided by 2.54, multiplied by DPI — for centimetres. For millimetres, divide by 25.4 instead. For inches, just multiply by DPI. So a 3.5 cm wide photo at 300 DPI is 3.5 ÷ 2.54 × 300 = 413 pixels. A 4.5 cm tall photo at the same DPI is 531 pixels. That is why Indian passport photos are commonly exported at 413 by 531 pixels, and why some portals round this to 420 by 540.
Common Indian document sizes at 300 DPI
| Document | Physical size | Pixels at 300 DPI |
|---|---|---|
| Indian passport photo | 3.5 × 4.5 cm | 413 × 531 |
| PAN card photograph | 2.5 × 3.5 cm | 295 × 413 |
| Signature strip | 3.5 × 1.5 cm | 413 × 177 |
| Stamp size photo | 2 × 2 cm | 236 × 236 |
| US visa photo | 2 × 2 inch | 600 × 600 |
| Schengen visa photo | 3.5 × 4.5 cm | 413 × 531 |
| Standard photo print | 4 × 6 inch | 1200 × 1800 |
| A4 sheet | 21 × 29.7 cm | 2480 × 3508 |
Which DPI should you choose?
For anything that will be printed and inspected — passports, visa photos, ID cards — use 300 DPI. It is the long-standing standard for photo printing and is what most government portals assume. Use 600 DPI only when a printer explicitly asks for it, because the file becomes four times larger for a difference most people cannot see. For screen-only use, 72 or 96 DPI is enough; the pixel count is what matters on a screen, and the DPI value is metadata that browsers ignore.
Locking the aspect ratio
With the lock on, changing one dimension recalculates the other so the picture is never distorted. This is what you want for portraits and photographs. Turn the lock off only when you deliberately need an exact shape — for example squeezing a wide signature scan into a narrow strip — and be aware that faces will stretch if the ratio is far from the original.
Adding a file-size limit at the same time
Many portals combine a physical size with a byte limit: "3.5 × 4.5 cm and under 50 KB". Fill in the optional KB field and the tool resizes first, then searches for the highest JPEG quality that fits the limit. Doing both in one pass avoids the usual cycle of resize, download, check size, and resize again.
Why resizing up never adds detail
If your source photo is smaller than the target pixel size, the tool has to invent pixels by interpolation. The result is smooth but not sharper — you cannot recover detail that was never captured. Always start from the largest original you have. If the only copy is a small WhatsApp image, consider rescanning or re-photographing rather than upscaling.
Frequently asked questions
How many pixels is 3.5 cm by 4.5 cm at 300 DPI?
413 by 531 pixels. The calculation is 3.5 ÷ 2.54 × 300 for the width and 4.5 ÷ 2.54 × 300 for the height.
What DPI should I use for a passport photo?
300 DPI is the standard for photo printing and is what most Indian passport and visa portals assume. Use 600 DPI only if a printer specifically requests it.
Can I resize to both a physical size and a KB limit?
Yes. Set the width, height, unit and DPI, then enter a KB value in the optional compression field. The tool resizes first and then compresses to fit.
Will resizing stretch my photo?
Only if you unlock the aspect ratio. With the lock on, the second dimension is recalculated automatically so the image keeps its shape.
Does resizing reduce quality?
Resizing down discards pixels but usually looks sharp. Resizing up interpolates new pixels, which softens detail — you cannot add information that was not in the original.
Is the image uploaded anywhere?
No. The resize happens on a canvas inside your browser. The file never leaves your device.
What is the difference between DPI and pixels?
Pixels are the actual grid of dots in the file. DPI describes how densely those pixels are packed when printed. The same 413-pixel-wide file is 3.5 cm wide at 300 DPI and 7 cm wide at 150 DPI.
Pixels, centimetres and inches are three different questions
A form asks for a photo 3.5 cm wide. Your phone only knows pixels. Somewhere in between sits DPI, the number that decides how many pixels get squeezed into one inch of paper. Get that number wrong and a photo that looks perfect on screen prints at the wrong size — usually too small, with a white border where the printer ran out of image.
The arithmetic is not hard once you see it. One inch is 2.54 cm. At 300 DPI there are 300 pixels in every inch, so 3.5 cm becomes (3.5 ÷ 2.54) × 300, which is 413 pixels. At 200 DPI the same 3.5 cm is 276 pixels. Both are “correct” in the sense that they describe 3.5 cm, but only the 300 DPI version has enough detail to print cleanly. Indian ID forms are almost always designed around 300 DPI, which is why 3.5 by 4.5 cm passport photos are 413 by 531 pixels everywhere you look.
The other half of the problem is aspect ratio. If you force a square photo into a 3.5 by 4.5 frame without cropping, faces stretch. Always crop to the target ratio first, then scale. That is the difference between a photo that looks like you and one that looks like a distorted version of you.
Fix it in this order
- Use 300 DPI for anything that will be printed or pasted on a form.
- Use 72–96 DPI only for screens and websites.
- Crop to the target ratio before resizing, never after.
- Keep the original file. Resizing up never adds detail back.
- For social media, match the platform's own numbers rather than a round guess.
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