A single notice can say the photo must be 3.5 × 4.5 cm, 200 × 230 pixels, 20–50 KB and sometimes 200 DPI — four numbers that look like they describe the same thing but measure four different things. Once you know which is which, every form's rule becomes easy to meet, and you'll know which one the portal can actually check.
| Measurement | What it describes | Changed by | Checked by portals? |
|---|---|---|---|
| Pixels (px) | How many dots the image has | Resizing, cropping | Often — most bank and state portals |
| cm / inches | How big it prints | Pixels and DPI together | Never directly |
| DPI | A tag saying how densely to print | Editing the tag | A few (PAN, DSSSB, IBPS thumb) |
| KB | Disk space the file takes | Pixels and compression | Almost always |
Pixels: how many dots the image has
Pixels are the grid of coloured dots an image is made of. 200 × 230 px means 200 columns and 230 rows — 46,000 dots in total. Pixel dimensions are the only size that is a property of the image itself, and portals that "check the dimensions" are checking this number.
A phone photo is about 4000 × 3000 px, roughly 260 times as many dots as a 200 × 230 exam photo. Shrinking pixels throws away detail nobody will see at the size the form displays; enlarging them invents dots and looks soft. When a form names pixels, resize to exact pixels and crop so the shape matches.
Centimetres and inches: how big it prints
A digital image has no physical size until it is printed. 3.5 × 4.5 cm only becomes pixels once you choose a density: at 300 DPI it is 413 × 531 px, at 200 DPI 276 × 354 px, at 72 DPI 99 × 128 px. Without a DPI, a centimetre size is incomplete.
When a form gives only centimetres, 300 DPI is the safe assumption — it is the print standard for passport photos, and our cm resizer uses it unless you change it. The pixels ↔ cm converter does the arithmetic both ways.
DPI: the number that links pixels and cm
DPI (dots per inch) is a tag stored inside the file that says how densely to print the pixels. Changing it does not change the pixels or the KB: a 413 × 531 image stays 413 × 531 whether the tag says 72 or 300 — it just prints 14.6 cm or 3.5 cm wide.
Strictly, a screen image has PPI (pixels per inch) and DPI belongs to printers, but forms use the words interchangeably. A few portals read the tag: Protean PAN wants 200, DSSSB 96, the IBPS thumb impression and declaration 200. If yours does, the DPI converter sets the tag without touching a single pixel — no quality loss.
How do you convert cm to pixels?
Divide the centimetres by 2.54 to get inches, then multiply by the DPI: pixels = cm ÷ 2.54 × DPI. So 3.5 cm at 300 DPI is 3.5 ÷ 2.54 × 300 ≈ 413 px. Going the other way, cm = pixels ÷ DPI × 2.54. Round to the nearest whole pixel.
| Size | 72 DPI | 200 DPI | 300 DPI |
|---|---|---|---|
| 3.5 × 4.5 cm (passport, CTET) | 99 × 128 px | 276 × 354 px | 413 × 531 px |
| 2 × 2 in (US passport) | 144 × 144 px | 400 × 400 px | 600 × 600 px |
| 6 × 2 cm (SSC signature) | 170 × 57 px | 472 × 157 px | 709 × 236 px |
| 3.5 × 2.5 cm (PAN photo) | 99 × 71 px | 276 × 197 px | 413 × 295 px |
Notices sometimes give both and they don't quite agree. IBPS describes its 200 × 230 px photo as a 4.5 × 3.5 cm passport photo; that works out to roughly 130–145 DPI depending on which side you measure — a sign the pixels are the real rule and the centimetres a description.
KB: how much disk space the file takes
File size depends on pixels and on how hard the JPEG is compressed. A 413 × 531 photo can be 30 KB or 300 KB depending on quality and detail. That's why a form can demand both 200 × 230 px and 20–50 KB: the first fixes the pixels, the second the compression.
Portals count 1 KB as either 1,000 or 1,024 bytes, so aim slightly under any maximum and slightly over any minimum. Compress to an exact KB, and see what "20 KB" actually means for why a phone photo starts at megabytes.
Putting it together: a worked example
Say a notice asks for a 3.5 × 4.5 cm photo at 200 DPI, 20–50 KB. Convert first: that's 276 × 354 px. Crop and resize to exactly that, set the DPI tag to 200, then compress into the 20–50 KB band. All four numbers are now met.
- Work out the pixels: 3.5 ÷ 2.54 × 200 = 276, 4.5 ÷ 2.54 × 200 = 354.
- Crop to the face and resize to 276 × 354 with the cm resizer set to 200 DPI — it writes the tag as well.
- Compress into the band, aiming for the middle (say 35 KB).
- Run the file through the photo checker to confirm pixels, DPI, KB and format before uploading.
For the step-by-step method of shrinking a big photo — resize first, then compress — see how to reduce image size. If a file meets every number and still fails, work through why exam photos get rejected.
Frequently asked questions
- What does 200 × 230 pixels mean in cm?
- 1.69 × 1.95 cm at 300 DPI, 2.54 × 2.92 cm at 200 DPI, or 7.06 × 8.11 cm at 72 DPI. Pixels only have a physical size once you pick a DPI.
- How many pixels is a 3.5 × 4.5 cm passport photo?
- 413 × 531 px at 300 DPI, the print standard most passport and exam resizers use. At 200 DPI it is 276 × 354 px.
- Does changing DPI reduce quality or file size?
- No. DPI is only a tag; the pixels and the KB stay the same. It changes how large the image prints, not how sharp it is on screen.
- Can I increase pixels without losing quality?
- Not really — upscaling invents dots. Start from the original camera photo (thousands of pixels) and shrink it to the target; never enlarge a small file.