BMP is Windows' basic bitmap that stores pixels as they are, without compression. BMP opens in most environments, but another format such as ICO may suit some uses better.
ICO is a container format for favicons and Windows icons. When you convert BMP to ICO, you get a format that supports transparency and it can be used as an icon or favicon. See the comparison below for what changes.
This converter reads the file itself to confirm it is BMP, then converts it to ICO right in your browser. Your image is never uploaded.
BMP vs ICO: what's the difference?
| Item | BMP | ICO |
|---|---|---|
| Compression | None (uncompressed) | Lossless |
| Transparent background | No | Yes |
| Animation | No | No |
| Introduced | 1990 | 1985 |
| Support in programs and upload forms | broad | moderate |
| Shown directly in browsers | Yes | Yes |
| Photo file size (JPG = 1) | about 12× | n/a |
What is BMP?
BMP is a bitmap format from Windows that mostly stores pixel values as they are, without compression. Its simple structure makes it easy for programs to read, but the files are so large that it is rarely used on the web.
What is ICO?
ICO is the format used for Windows icons and website favicons. Its distinguishing feature is that one file can hold several sizes, such as 16×16, 32×32 and 256×256.
What changes when you convert BMP to ICO
Converting doesn't add a transparent background
BMP has no transparency information, so converting to ICO keeps the background as it is. To remove a background you need a separate background-removal tool.
Pixel values are preserved exactly
BMP and ICO are both lossless, so there is no change in quality. Only the file structure, compatibility and size differ.
It is fitted into a square of at most 256×256
ICO is limited to 256×256. Larger images are scaled down with their aspect ratio kept, and images that aren't square are centered with the leftover area left transparent.
ICO has no quality setting
ICO is lossless, so the quality slider doesn't apply. Instead, when converting from BMP you can manage file size by resizing (exact width and height, or a percentage).
How the file size changes
ICO holds images of up to 256×256, so a large original shrinks a lot. If the image is already small, the difference is negligible.
ICO has narrower support than BMP
BMP support is broad and ICO support is moderate. Check that the recipient can open ICO first, and if you're not sure, JPG or PNG is safer.
When to convert
- You're making a website favicon or a Windows shortcut icon
- You're preparing an image for typical ICO uses (website favicons, windows program icons)
- You want to tidy a BMP file into a format that's easier to edit or archive