Convert BMP to ICO (favicon)
A bit of format trivia: an ICO file is essentially a directory of BMPs — the icon entries inside use the same bitmap structure Windows has read since 1990. So this conversion is pleasingly circular: your bitmap is center-cropped square, scaled to 16, 32 and 48px, and filed into the container it was always destined for.
Also useful: Convert PNG to ICO (favicon)
How it works
Drop the bitmap in; retro assets and legacy exports are exactly what this pairing was made for.
Pixels transfer straight into 16, 32 and 48px icon entries — the same structure Windows has parsed since 1990.
Remember standard BMPs are opaque, so expect a full square icon; download the .ico alone or zipped with others.
BMP vs ICO
These two are practically family — ICO entries are BMP structures inside a directory — so this is the most literal conversion on the site. Family resemblance has limits though: classic 24-bit bitmaps bring no alpha, so PNG-sourced icons keep the prettier corners.
| BMP | ICO | |
|---|---|---|
| Compression | Usually none (raw pixels) | Lossless (BMP or PNG entries) |
| Transparency | No | Yes (full alpha) |
| Animation | No | No |
| Support | Universal on desktop | Universal for favicons |
| Best for | Legacy Windows software, raw pixel exchange | Favicons and Windows app icons |
Frequently asked questions
No — that is the whole reason I built this. The conversion runs in your browser using WebAssembly, so your files never leave your device; there is no server in the loop at all. It also means the tool keeps working offline once the page has loaded, and there is no file size limit beyond your device’s memory.
No, and it is a common trap — an ICO needs a header directory describing each icon entry, which a renamed BMP lacks. Some viewers tolerate the trick; Windows shortcuts and browsers generally do not. This tool builds the real structure, with the three standard sizes inside.
Yes — it is exactly how you turn legacy art assets into program icons. The 32-bit entries this tool writes work on everything from Windows XP onward. One note for retro-computing projects: truly ancient software may expect 8-bit palettized icons, which is a different beast.
Almost never — standard BMPs are fully opaque, so your icon will be a solid square. That is fine for photographic or full-bleed icons. If you need transparent corners, recreate the source as a PNG with alpha and use PNG to ICO instead.
It is the most literal path there is: ICO entries are BMP structures internally, so the pixels transfer without any format gymnastics. Better, though? Only if the BMP is 32-bit. Classic 24-bit BMPs carry no alpha, so PNG sources produce icons with proper transparent corners while BMP sources produce solid squares. Literal is not always prettier.
Transparency, in practice — standard bitmaps have no alpha channel, so the icon occupies its full square on every background. For a full-bleed design that is invisible; for a round or irregular mark it means a visible box in dark-mode tabs. The fix is upstream: rebuild the source with alpha, then convert that instead.
Related tools
Convert PNG to ICO (favicon)
Convert PNG to a multi-size ICO favicon in your browser — free, no upload. One file with 16, 32 and 48px icons with full alpha, ready for any site root.
Convert GIF to ICO (favicon)
Convert GIF to ICO in your browser — free, private, no upload. The first frame becomes a 16, 32 and 48px favicon in one file — a natural fit for pixel art.
Convert BMP to PNG
Convert BMP to PNG in your browser — free, lossless, private, no upload. Cut uncompressed bitmaps down by 50–90% without touching a pixel — no tradeoff.
Convert BMP to JPG
Convert BMP to JPG in your browser — free, private, no upload or signup. Giant uncompressed bitmaps become shareable photos, typically 95–98% smaller.