Photo size in KB vs pixels — simple explanation
Exam notices mix three kinds of numbers: KB, pixels and centimetres. “Photo 200 × 230 pixels, 20–50 KB.” “Signature 6.0 × 2.0 cm.” “Photo 10–200 KB.” It is easy to think they are the same thing. They are not — and mixing them up is the reason for many “image size too large” errors.
This guide explains each one in plain words, with the real numbers exam portals use.
The short answer
- Pixels = how big the picture is (width × height of tiny dots). Example: 200 × 230 px.
- KB = how heavy the file is on disk. Example: 35 KB.
- cm + DPI = the printed size, which turns into pixels once you know the DPI.
A portal can check both pixels and KB. Fixing one does not fix the other.
What is a pixel?
Every digital photo is a grid of tiny coloured squares called pixels. A phone photo might be 3000 × 4000 px — that is 12 million pixels (12 MP). An IBPS photo is 200 × 230 px — only 46,000 pixels.
When a notice says 200 × 230 pixels, it means the image must be 200 pixels wide and 230 pixels tall. Width comes first.
The shape matters too. 200 × 230 is slightly taller than wide. A phone selfie (3:4) is much taller. If you only resize without cropping, the face gets squashed or stretched. Always crop to the right shape first.
What is a KB?
KB (kilobyte) measures file size — how much storage the file takes. Most portals count 1 KB = 1,024 bytes, but some count 1,000.
So the safe reading of “20–50 KB” is at least 20,480 bytes and at most 50,000 bytes. SahiSize aims just under the top of that, with a small safety margin, so the file passes either way.
File size depends on:
- Pixel count — more pixels usually means more KB.
- JPG quality — higher quality keeps more detail and makes a bigger file.
- Detail in the picture — a busy background or grainy low-light photo makes a bigger file than a plain white wall.
This is why two photos of exactly 200 × 230 px can be 18 KB and 60 KB. Same pixels, different KB.
Why pixels do not fix KB (and the other way round)
Say IBPS wants 200 × 230 px and 20–50 KB. You resize your photo to 200 × 230. The file is now 62 KB. Still rejected — “image size too large”.
Or you compress a 2 MB photo to 40 KB in some app, but it is still 1200 × 1600 px at very low quality. KB is fine, pixels are wrong, and the face looks blotchy.
The right way: crop to the shape, resize to the exact pixels, then adjust JPG quality until the KB lands inside the range. The exam pages and Custom size do all three in one go. Resize Image does the last two, so crop first if the shape is different.
Centimetres and DPI: turning cm into pixels
Some notices give a physical size, like SSC’s signature “6.0 cm × 2.0 cm”, or “photo 3.5 × 4.5 cm”. A file on a screen has no centimetres — so you need DPI (dots per inch) to convert.
The formula:
pixels = cm ÷ 2.54 × DPI
(2.54 because one inch is 2.54 cm.)
Worked examples:
| Physical size | DPI | Pixels |
|---|---|---|
| 3.5 × 4.5 cm (passport photo) | 200 | ≈ 276 × 354 px |
| 3.5 × 4.5 cm | 300 | ≈ 413 × 531 px |
| 6.0 × 2.0 cm (SSC signature) | 200 | ≈ 472 × 157 px |
| 3.5 × 1.5 cm (CTET signature) | 200 | ≈ 276 × 118 px |
| 10 × 5 cm (bank declaration) | 200 | ≈ 787 × 394 px (notice says 800 × 400) |
So for SSC CGL, the 6.0 × 2.0 cm signature becomes about 472 × 157 px at 200 DPI — that is the size SahiSize uses by default. For CTET, the 3.5 × 4.5 cm photo becomes 276 × 354 px.
If you want to do your own conversion, Resize Image accepts cm, inches or pixels, plus DPI.
Does DPI change the KB?
Not by itself. The DPI value is just a label stored inside the JPG. A 200 × 230 px image is the same file whether it says 72 DPI or 200 DPI. What matters is the pixels.
A few portals do read the DPI label (India Post GDS asks for 72–150 DPI), so SahiSize writes the correct DPI into the file anyway.
KB-only exams
Many exams give only a KB range and no pixel size:
- NEET UG, JEE Main, CUET UG, UGC NET, CSIR NET — photo 10–200 KB.
- REET — photo 20–50 KB.
- UPSC CSE, NDA, CDS — photo 20–200 KB.
Here you have freedom with pixels. Keep a normal passport shape (3.5 × 4.5 cm aspect) and a sensible size like 413 × 531 px, then fit the KB. Do not upload a 4000 px photo just because no pixels are listed — it will be far above 200 KB.
Common numbers at a glance
Always check the latest official notice — these are from recent notices and can change between cycles.
| Exam | Photo | Signature |
|---|---|---|
| IBPS PO, SBI, RBI | 200 × 230 px, 20–50 KB | 140 × 60 px, 10–20 KB |
| SSC CGL, CHSL, MTS | Live capture | 6.0 × 2.0 cm ≈ 472 × 157 px, 10–20 KB |
| NEET UG | 10–200 KB (no pixels) | 10–100 KB |
| CTET | 3.5 × 4.5 cm ≈ 276 × 354 px, 10–100 KB | 3.5 × 1.5 cm, 3–30 KB |
| India Post GDS | 320 × 400 px, 30–100 KB | 300 × 120 px, 20–100 KB |
How to get both right in 4 steps
- Open your exam page on SahiSize, or Custom Preset if your exam is not listed.
- Pick your photo and crop it in the locked box (the shape is already set).
- Let auto-fit set the pixels and find the best JPG quality inside the KB range.
- Check the three ticks — pixels, KB, format — then download.
Need only a KB target, like “photo 20 kb”? Use Compress Image or the ready page compress to 20 KB. More on that in how to reduce photo size to 20 KB on mobile.
FAQ
My phone shows the photo as “2.4 MB”. How many KB is that?
About 2,458 KB (2.4 × 1,024). IBPS allows at most 50 KB, so it must become roughly 50 times smaller.
Can I just change the DPI to reduce the KB?
No. DPI is a label. To reduce KB, you reduce pixels or JPG quality. Changing only the DPI leaves the file almost the same size.
The notice says 4.5 × 3.5 cm but also 200 × 230 px. Which one?
Upload the pixel size the portal asks for. Banking notices mention both: the cm is the printed photo size, the pixels are what the portal checks.
Why does my resized photo look blurry?
You probably shrank it too much and then stretched it back up, or the KB limit forced very low quality. Start from the original camera photo, not a WhatsApp copy, and crop before resizing.
Is SahiSize linked to IBPS, SSC or NTA?
No. SahiSize is an independent tool. Always check the latest official notice for your exam. Your photos are processed on your own device and never uploaded.