Photo size in pixels, cm and DPI — what forms really mean
3.5 × 4.5 cm, 200 × 230 pixels, 200 DPI — what these numbers mean and how to turn centimetres into pixels for a form.
Pixels
A digital photo is a grid of dots called pixels. "200 × 230" means 200 dots wide and 230 dots high.
Centimetres and DPI
Centimetres describe the printed size. DPI (dots per inch) links the two: pixels = cm ÷ 2.54 × DPI. At 300 DPI a 3.5 × 4.5 cm photo is 413 × 531 pixels; at 200 DPI it is 276 × 354 pixels.
KB is something else
KB is the file size on disk. Two photos with the same pixels can have very different KB depending on compression.
Do it in one step
Exam form photo & signature takes width, height and the KB range together and gives you exactly that.