Notifications mix units freely: "3.5 cm × 4.5 cm", "200 × 230 pixels", "20 KB to 50 KB", "scanned at 200 DPI". They measure different things. Once you know which is which, meeting any requirement becomes straightforward.
Pixels — the image's dimensions
A digital photo is a grid of dots called pixels. "200 × 230 pixels" means 200 dots wide and 230 tall. This is what upload portals actually check, because a file has no physical size until it is printed. Width always comes first.
KB — the file size
KB (kilobytes) is how much storage the file takes. It depends on the pixel count and on JPG compression quality. The same 200×230 photo can be 15 KB or 80 KB depending on quality. That is why you control KB by adjusting compression after setting the pixels.
Rough guide: a 200×230 photo at good quality is 15–35 KB; a 1200×1200 photo (CAT) is 150–400 KB before compression.
cm and inches — the printed size
"3.5 × 4.5 cm" is the classic Indian passport photo size on paper. On a screen it has no meaning until you choose a DPI.
DPI — the bridge between cm and pixels
DPI (dots per inch) says how many pixels fit in one inch (2.54 cm) when printed. The formula is:
pixels = cm ÷ 2.54 × DPI
Worked examples for 3.5 × 4.5 cm:
| DPI | Width (3.5 cm) | Height (4.5 cm) |
|---|---|---|
| 100 | 138 px | 177 px |
| 200 | 276 px | 354 px |
| 300 | 413 px | 531 px |
That is why NTA's 3.5×4.5 cm photo works out to about 275×354 px at 200 DPI, and SSC's long-standing 275×354 px requirement is the same shape.
Which number should you follow?
- If the notification gives pixels, match them exactly.
- If it gives only cm/inches, keep the same shape (aspect ratio) and use 200 DPI unless another DPI is stated.
- Always meet the KB range — it is checked on every upload.
- Always save as JPG unless told otherwise.
The cm / inch / mm resizer converts physical sizes to pixels for you, and every exam page in the size chart lists the exact pixels.