Convert BMP to ICO
Output is typically about 100% smaller.
- Files stay on your device
- Free, no sign-up
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Will converting BMP to ICO make the file smaller?
Usually, yes. A 12-megapixel photo is around 36 MB as BMP and around 100 KB as ICO — about 100% smaller. Because ICO is lossless the result depends entirely on the image content — flat colour and text compress far better than photographic detail.
Does converting BMP to ICO lose quality?
No. ICO is lossless, so every pixel decoded from your BMP file is stored exactly. Both formats are lossless, so the conversion is pixel-for-pixel identical.
Is transparency preserved when converting BMP to ICO?
Yes. Both BMP and ICO support an alpha channel, so transparent and semi-transparent pixels carry across unchanged — a logo with a cut-out background stays cut out, and soft drop shadows keep their gradient rather than picking up a white halo. Because ICO is lossless, the alpha channel is stored exactly as it was.
What size should a favicon be?
Start from a square source image of at least 256 × 256 pixels. An ICO bundles several resolutions in one file — 16, 32, 48 and 256 pixels covers browser tabs, bookmarks and Windows shortcuts. Modern sites usually pair favicon.ico with a 180 × 180 PNG for Apple touch icons and an SVG for scalable tab icons.
What sizes are in the ICO file?
Four — 16, 32, 48 and 256 pixels — packed into a single file, each stored as PNG. That is the point of the format: the browser or operating system picks whichever size it needs, so one favicon.ico covers tab icons, bookmarks and Windows shortcuts. Non-square images are centred rather than stretched, so start from a square source if you can.
How it works, and more about bmp to ico
How it works
- Add your BMP file. Drag a BMP file onto the drop zone, or click to browse. You can select several at once.
- Choose your settings. ICO is lossless, so there is nothing to configure — the output matches the input pixel for pixel.
- Download the ICO. Conversion runs on your device as soon as each file is added — no upload, no queue. Download each result when it is ready.
BMP and ICO side by side
| BMP | ICO | |
|---|---|---|
| Full name | Bitmap Image File | Windows Icon |
| Compression | Lossless | Lossless |
| Transparency | Yes — alpha channel | Yes — alpha channel |
| Animation | No | No |
| Browser support | Supported in all major browsers, though rarely used on the web | Universal for favicons |
| Typical 12 MP photo | ~36 MB | ~100 KB |
| Usually used for | Legacy Windows applications, scanners and embedded displays | Website favicons and Windows application icons |
On a typical 12-megapixel phone photo, the ICO output comes out about 100% smaller than the BMP original. These are order-of-magnitude figures for one kind of image — your own results will vary a great deal, because flat colour, text and line art behave nothing like photographic detail.
What this tool actually produces
Not estimates. Each row below was produced by running the file through this page in a real browser and measuring the result, at the default quality of 82.
| Test image | BMP in | ICO out | Change |
|---|---|---|---|
| UI screenshot 1440 × 900, dense text on flat panels — the hardest case for JPEG | 3.7 MB | 22 KB | -99% |
| Line-art diagram 1200 × 800, hard edges and large flat areas | 3.7 MB | 9 KB | -100% |
Every test image got smaller, though by very different margins — flat colour and text behave nothing like photographic detail, so treat the closest row to your own content as the useful one. Measured in Chrome 150.0.7871.46; other browsers encode slightly differently.
What to watch out for
- Only practical at small icon sizes
- Obsolete for general imagery
- Modern sites increasingly prefer SVG or PNG favicons
About the two formats
BMP stores pixels essentially uncompressed, which makes it enormous — a 12-megapixel photo lands around 36 MB, roughly 11× the same image as a JPEG. It persists mainly inside legacy Windows software, scanning utilities and embedded systems where decoding simplicity beats file size.
ICO is a container rather than a codec: it bundles the same icon at several sizes — typically 16, 32, 48 and 256 pixels — so the operating system or browser can pick the right one. Its remaining job is the favicon at the root of a website, and Windows application icons.
Other conversions
Everything runs on your device — nothing is uploaded, so there is no size limit, no queue and no copy left on a server afterwards. There is more on how browser-based conversion works if you want the detail. Otherwise, browse every image tool, or convert ICO back to BMP.