Pixels, DPI and KB: What Online Forms Actually Ask For
Dimensions, resolution and file size are three different things. Learn what each one means so you can meet any photo requirement first time.
Photo requirements often mix several numbers — "200 × 230 pixels, 300 DPI, between 20 and 50 KB". These describe different properties of the image, and changing one does not automatically fix the others. Understanding the difference saves a lot of trial and error.
Dimensions (pixels)
Dimensions are the width and height of the image in pixels. They define the image’s shape and how much detail it can hold. When a form asks for exact pixel dimensions, the uploaded image must match them precisely, and the shape (aspect ratio) must match too — otherwise the photo will be stretched or rejected.
DPI (dots per inch)
DPI only matters when an image is printed. It is a label stored in the file that tells a printer how many pixels to place in each inch of paper. Changing the DPI value alone does not change the image or its file size. It becomes important when a requirement is given in millimetres or inches: a 35 × 45 mm photo at 300 DPI needs 413 × 531 pixels.
File size (KB)
File size is how much storage the image takes. It depends on the dimensions, the format and the compression quality. Two images with identical dimensions can have very different file sizes — a photo with lots of fine texture compresses less than one with a plain background.
| Requirement says | What to change | PhotoSize tool |
|---|---|---|
| "Maximum 50 KB" | Compression quality, then dimensions | Compress to KB |
| "200 × 230 pixels" | Exact dimensions (and crop to the right shape) | Form Ready Photo |
| "35 × 45 mm, 300 DPI" | Dimensions in mm with DPI | Passport / ID Photo |
| "JPG only" | Format | Convert Image |
Meeting several requirements at once
The Form Ready Photo tool combines everything in one step: enter the exact dimensions (in pixels, millimetres, centimetres or inches), choose how to fit the photo into that shape, set the maximum file size and the format. The result screen checks each requirement and marks it with a green tick when it is met.
Tip: Crop to fill is usually the right choice for portraits: it fills the exact shape and trims a little from the edges, instead of stretching the face or adding borders.