Photo Size in KB vs Pixels: What Forms Actually Ask For

A notification might say: “Photograph: 3.5 cm × 4.5 cm, 200 × 230 pixels, file size 20 KB to 50 KB, JPG.” That is three different measurements of one photo. Knowing what each means is the difference between a form that uploads first time and an evening of “invalid file” errors.

Pixels: the photo’s dimensions

A digital photo is a grid of tiny dots called pixels. 200 × 230 pixels means 200 dots wide and 230 dots tall. A modern phone photo is around 3000 × 4000 pixels, far bigger than any form needs. Pixels decide the photo’s shape (its aspect ratio) and how much detail it can hold.

KB: the file’s weight

KB (kilobytes) measure how much storage the file takes. 1 MB is 1,024 KB. A form asks for a KB range so its servers stay fast and photos stay readable. The same 200 × 230 photo can be 8 KB or 80 KB depending on how strongly the JPG is compressed and how busy the picture is. A plain white background compresses to fewer KB than a patterned wall.

The key point: pixels and KB are independent. Reducing pixels usually reduces KB, but you cannot reach an exact KB range just by picking pixels. You set the pixels first, then adjust JPG quality until the file lands in the range. That second step is what “compress to KB” tools do.

Centimetres and dpi: the printed size

Centimetres describe how big the photo would be on paper. To turn centimetres into pixels you need the dpi (dots per inch): pixels = cm ÷ 2.54 × dpi. For a 3.5 × 4.5 cm passport photo:

• at 200 dpi: 276 × 354 pixels (what SSC uses),
• at 300 dpi: 413 × 531 pixels (what NTA exams and most passport photo tools use).

When a form gives centimetres and pixels, follow the pixels. When it gives only centimetres, 300 dpi is the safe choice unless the KB limit is very small.

How to hit all three at once

1. Crop the photo to the right shape (the ratio of the pixels or centimetres).
2. Resize to the exact pixels.
3. Save as JPG, raising or lowering quality until the file is inside the KB range; aim for the upper half for the best clarity.

On PixFit each exam page has these numbers preset, so steps 1 to 3 happen together, in your browser. Need a size we do not have yet? Use Resize image for any pixels, or Compress image to KB for a KB limit only. Every exam’s numbers are in the exam photo size database.

Quick reference

• Pixels set the shape and detail. Check the notification for exact width × height.
• KB sets the file weight. Most exams: photo 20–50 KB, signature 10–20 KB.
• cm × dpi ÷ 2.54 = pixels. 3.5 × 4.5 cm = 276 × 354 px (200 dpi) or 413 × 531 px (300 dpi).