Aadhaar and passport photo size: cm, mm, and pixels explained
Almost every Indian exam form and government portal asks for a photo sized "3.5 x 4.5 cm," but the file you actually upload is measured in pixels, and different portals expect different pixel counts for that same physical size. This page works through why, with the actual conversion math, so you can figure out the right pixel size for a form that gives you a DPI figure, a cm or mm measurement, or nothing more specific than "passport size." If you already know your target pixel dimensions, the cropping tool on the homepage handles the rest.
Why "3.5 x 4.5 cm" isn't one pixel size
A centimeter is a unit of physical length. A pixel is a unit of image resolution. The two only line up once you fix a third number: DPI, dots per inch, which is how many pixels the image packs into each inch of physical size. Change the DPI and the same 3.5 x 4.5 cm photo comes out as a different pixel grid, even though it would print at exactly the same size on paper.
The conversion itself is simple. An inch is 2.54 cm, so a length in centimeters converts to inches by dividing by 2.54, and then to pixels by multiplying by the DPI:
pixels = (centimeters ÷ 2.54) × DPI
Run 3.5 cm and 4.5 cm through that formula at 200 DPI and you get about 276 x 354 px. Run the same two numbers at 300 DPI and you get about 413 x 531 px. Both are correct descriptions of a 3.5 x 4.5 cm photo. Neither is "the" pixel size for it, because there isn't one without picking a DPI first. This is exactly why our SSC preset lists 413 x 531 px as the 300 DPI figure but notes that some SSC notifications specify 200 DPI instead, which works out to roughly 276 x 354 px for the same physical photo.
3.5 x 4.5 cm at common DPI values
If your form states a DPI that isn't covered by name anywhere else on this site, use this table, or the formula above, to work out the pixel size yourself.
| DPI | 3.5 cm width | 4.5 cm height | Pixel size |
|---|---|---|---|
| 150 DPI | 207 px | 266 px | 207 × 266 px |
| 200 DPI | 276 px | 354 px | 276 × 354 px |
| 300 DPI | 413 px | 531 px | 413 × 531 px |
3.5 cm and 4.5 cm are the same physical size as 35 mm and 45 mm, so if a form states the size in millimeters instead of centimeters, this table still applies directly. Figures are rounded to the nearest whole pixel.
Pixel size and file size (KB) are two separate rules
Most exam portals set two limits on a photo upload, not one: a pixel dimension (or a range) and a file size range in KB. It's easy to assume these move together, but they don't. Pixel dimensions describe how much detail the image holds, its width and height in a fixed grid. File size in KB describes how much storage the compressed file takes up on disk. A photo can be resized to exactly 413 x 531 px and still weigh 8 KB or 300 KB, depending entirely on how hard it's been compressed.
JPEG compression works by discarding some visual detail to shrink the file, and the amount discarded is controlled by a quality setting, not by the pixel grid. Lower the quality and the file gets smaller without the width or height changing at all. Push it too far and the photo starts to show blotchy patches and soft edges, but the dimensions on paper stay 413 x 531 px the whole time. That's the gap that trips people up: a photo that's the right pixel size can still get rejected for being outside the KB range, and resizing it again won't fix that, only re-compressing it will.
Practically, this means a correct upload has to satisfy both constraints at once: resized to the pixel dimensions the form asks for, and compressed to land inside its KB range. The cropper on this site's homepage handles both steps together, it crops to a chosen preset's pixel size and then adjusts JPEG quality until the output file lands inside the target KB range, without touching the width or height again once it's set.
Exam-specific pixel and KB requirements
Once you know which pixel size and KB range your form actually needs, use the matching guide below. Each one has the current figures we've checked, along with the cropping tool preset already set to that size.
| Exam category | Photo size | File size | Guide |
|---|---|---|---|
| SSC | 413 × 531 px | 20-50 KB | SSC |
| Bank / IBPS | 200 × 230 px | 20-50 KB | Bank/IBPS |
| UPSC | 413 × 531 px | 20-200 KB | UPSC |
| Railway (RRB) | 320 × 240 px | 30-100 KB | RRB |
Figures change with each exam notification. Confirm against your own official notification before submitting, and re-check the linked guide if it's been a while since it was last verified.
Frequently asked questions
Why do two exam forms ask for different sizes for what looks like the same photo?
Because "3.5 x 4.5 cm" describes a physical print size, not a pixel count, and each portal converts that physical size to pixels using its own assumed DPI. A portal built around 200 DPI will ask for roughly 276 x 354 px, while one built around 300 DPI will ask for roughly 413 x 531 px, even though both are describing the same 3.5 x 4.5 cm photo. The photo itself doesn't need to change, only the pixel dimensions you export at.
What DPI should I use if my form doesn't specify one?
If the form gives you a pixel size directly, use that and ignore DPI entirely, since DPI only matters for converting a physical size to pixels. If it only gives you a physical size like 3.5 x 4.5 cm or 35 x 45 mm with no DPI or pixel figure, 200 DPI is a reasonable default for government exam forms, since it's the more common baseline among the notifications we've checked. 300 DPI is the safer choice if the photo might also be printed, since it holds up better at print resolution.
Does reducing file size (KB) hurt photo quality?
Some quality loss is unavoidable once you compress a JPEG hard enough to hit a small KB target, but it doesn't happen right away. Reducing an already reasonably sized JPEG down to, say, 50 KB usually keeps a passport-style photo looking sharp on screen. The visible drop-off, blotchy skin tones, blurred edges around the face, tends to show up only once you push well below that, which is usually a sign the KB limit and the pixel dimensions are mismatched rather than that compression itself is the problem.
Know your target pixel size and KB range already? Skip straight to the homepage tool and crop your photo directly.
Guides by exam: SSC, bank exams, UPSC, and railway exams (RRB).