Why BMP files are absurdly large
BMP (bitmap) is a legacy Windows format that stores images with no compression at all — typically 3 bytes per pixel, every pixel. The math is brutal: a 1920×1080 screenshot is ~6 MB as BMP, ~150 KB as JPG, and often under 100 KB as WebP — all looking identical on screen.
BMPs usually come from old scanners, MS Paint, industrial software, or legacy export pipelines. There is almost never a reason to keep one: PNG stores the same pixels losslessly at a fraction of the size.
Which output should you pick?
| Your BMP contains | Convert to | Expected size |
|---|---|---|
| A photo or scan | JPG at 85% | ~2–5% of the BMP |
| A screenshot, diagram or text | PNG (pixel-perfect) or WebP | ~5–15% of the BMP |
| Anything for a website | WebP | smallest of all |
Lossless option: converting BMP → PNG loses zero image data — it is the same pixels stored sensibly. Choose PNG if you need a perfect copy.