Four ways to resize
| Option | Use it when | Example |
|---|---|---|
| Width × height, one box empty | You need a given width (or height) and the other side should follow | Width 1200, height empty → a 4000 × 3000 photo becomes 1200 × 900 |
| Width × height, both filled | A site or document needs an exact pixel size | 600 × 600 for a profile or ID photo |
| Percentage | You want everything a fixed amount smaller | 50% turns 3024 × 4032 into 1512 × 2016 |
| Longest side | A batch mixes portrait and landscape images | Longest side 1920: landscape becomes 1920 wide, portrait 1920 tall |
Sizes some platforms ask for
| Where | Size | Source |
|---|---|---|
| Instagram feed photo | Shared at up to 1080 px wide; ratios between 1.91:1 and 3:4 keep their shape | Instagram Help |
| YouTube custom thumbnail | 16:9; at least 640 px wide; 3840 × 2160 recommended; 2 MB limit when uploading from mobile | YouTube Help |
| US visa photo (DS-160) | Square, 600 × 600 to 1200 × 1200 px, JPEG up to 240 KB | U.S. Department of State |
| UK passport, online | At least 600 × 750 px, 50 KB to 10 MB | GOV.UK |
| IBPS PO/MT-XVI photo | 200 × 230 px preferred, 20–50 KB | IBPS notification |
All read on 21 October 2026. Platforms change their rules; check the current help page before a big batch.
When the shape doesn’t match
If you enter both a width and a height and the picture has different proportions, choose what should happen:
- Fit inside keeps the proportions; the result is at most that size (one side may be smaller).
- Fill exactly (crop the edges) fills the whole size and trims what sticks out, centred. Best for thumbnails and square profile pictures.
- Fill exactly (add a border) keeps the whole picture and fills the gap with a colour (Advanced → background).
- Stretch forces the size and distorts the picture. Rarely what you want.
To choose which part is kept rather than the centre, use Crop & rotate on the image first, or the crop tool.
Resampling quality
Resizing is done with a Lanczos3 filter in linear light (the same resizer Google’s Squoosh uses), not with the browser’s quick canvas scaling. Downscaled photos stay sharp, without the jagged edges or dark fringes that simpler scaling produces. Enlarging is possible but cannot add detail; by default smaller images are left as they are (untick “Never enlarge” to allow it).
Pixels, not DPI, decide how big an image looks on a screen. DPI only matters for printing or for forms that explicitly ask for it; you can set the DPI tag of JPG files under Advanced.
Resize and hit a file size at the same time
Enter the dimensions here and switch File size to Target size. Kilomill resizes first, then finds the best quality under your KB limit, which is what most application forms need (for example the US visa photo: square, at least 600 × 600 pixels and at most 240 KB).