KB vs Pixels vs DPI: What Photo Upload Forms Check
Does 200 DPI change the KB? How many pixels is 3.5×4.5 cm? Which number does the portal check? KB, pixels and DPI explained with worked examples.
By Venkatesh · Updated
Application forms describe photos with a mix of units — pixels, centimetres, KB and sometimes DPI. Understanding what each one means makes almost every upload problem easy to fix.
Pixels: the Size of the Image
A digital image is a grid of coloured dots called pixels. "200×230 pixels" means 200 dots wide and 230 dots tall. This is the number most portals check first. If the form says the photo must be exactly 200×230, a 201×230 image can be rejected.
Aspect ratio is the shape: width divided by height. 200×230 is a slightly tall rectangle; 400×400 is a square; a signature box such as 140×60 is wide and short. If you resize a photo to a different shape without cropping, it gets stretched.
KB: the Size of the File
KB (kilobytes) is how much storage the file takes. 1 KB = 1,024 bytes, and 1 MB = 1,024 KB. File size depends on the number of pixels, the JPEG quality, and how much detail the picture contains — a plain background compresses far better than a busy one.
Forms usually give a range, for example 20–50KB. Both ends matter: some portals reject files that are *too small* as well as too large, because a tiny file often means a blurry photo.
DPI: Only for Printing
DPI (dots per inch) tells a printer how many pixels to fit into an inch of paper. It is stored as a note inside the file and does not change the pixels or the KB. A 200×230 image is the same upload at 72 DPI or 300 DPI.
When a form mentions DPI together with centimetres (for example "3.5 cm × 4.5 cm at 200 DPI"), it is really describing a pixel size:
- 3.5 cm ÷ 2.54 × 200 ≈ 276 px
- 4.5 cm ÷ 2.54 × 200 ≈ 354 px
So "3.5×4.5 cm at 200 DPI" ≈ 276×354 pixels. Enter that pixel size in a resizer and ignore the DPI setting.
Reading a Requirement Line
| Requirement text | What to do |
|---|---|
| "200×230 pixels, 20–50KB, JPG" | Crop to exactly 200×230, save as JPG between 20 and 50KB |
| "Photo size should not exceed 50KB" | Any sensible size under 50KB; aim for 30–45KB |
| "3.5 cm × 4.5 cm" (no pixels) | Use the photo shape 7:9; a common pixel size is 413×531 at 300 DPI |
| "Signature 140×60 px, 10–20KB" | Sign in black on white paper, crop wide, save between 10 and 20KB |
| "Resolution 200 DPI" | Usually a hint about pixel size — follow the pixel numbers if given |
JPG, JPEG, PNG and HEIC
- JPG and JPEG are the same format with two spellings. Most portals require it.
- PNG is lossless and much larger for photos. Convert with PNG to JPG if the portal wants JPG.
- HEIC is the iPhone default and is rarely accepted. Convert with HEIC to JPG.
Changing only the file extension does not change the format. Always re-save the image.
PDFs Follow Similar Rules
Document uploads (certificates, caste or income certificates, marksheets) are often PDFs with a KB limit. A scanned page is mostly an image, so the same ideas apply: fewer pixels and lower image quality mean a smaller file. See How to Compress a PDF for an Online Application.
Quick Checklist
- Pixel width and height exactly as asked
- File size inside the KB range, with a small margin
- Correct format (usually JPG/JPEG)
- Correct shape — cropped, not stretched
- Plain background and sharp face
The exam directory lists commonly published sizes for many exams, but always confirm them in the current notification.