BMP to ICO Converter
Convert BMP to ICO in your browser. BMP files usually come from Windows Paint, legacy Windows programs, embedded displays and some scanners; ICO is the better fit for favicons and Windows icons. You get a multi-size ICO with PNG-compressed icons (16, 32, 48 and 256 px by default). Nothing is uploaded.
- Processed locally
- No upload, no wait
- No sign-up
- No watermark
Drop images here
or choose files · paste with Ctrl/⌘ V
BMP expected · other image formats also work
How to use BMP to ICO
- 1
Add your BMP files: drop them here, choose them, or paste from the clipboard.
- 2
Choose the icon sizes to include.
- 3
Click Convert. Each file is decoded and encoded in a background thread on this device.
- 4
Download the .ico files one at a time or together as a ZIP.
Why use Aback Images for bmp to ico
Where the ICO goes next
ICO opens in every browser (as a favicon), Windows and most Linux desktops.
ICO next to BMP
Both sides are lossless, so the size depends on how well the ICO encoder handles this picture compared with the BMP's usually none; RLE for some 4 and 8-bit files.
Written without a lossy pass
The ICO is written losslessly, so the pixels decoded from the BMP arrive unchanged.
Processed on your device
Your images are decoded, edited and encoded inside this browser tab by Web Workers. Nothing is uploaded to a server.
BMP vs ICO
What changes from BMP to ICO
Encoding: the BMP uses usually none; RLE for some 4 and 8-bit files; ICO uses each size stored as a headerless BMP or as a complete PNG, and the download is a multi-size ICO with PNG-compressed icons (16, 32, 48 and 256 px by default).
Bit depth: 1, 4, 8, 16, 24 or 32 bits per pixel in the BMP; ICO allows 1 to 32 bits per pixel, set per size, and the ICO written here has 32 bits per pixel.
Colour: RGB or an indexed palette in the BMP; ICO supports RGB or a palette, per image, written here as 8-bit sRGB.
Transparency: the BMP stores it as an optional fourth byte in 32-bit files, which many programs ignore; the ICO keeps it as 8-bit alpha in 32-bit and PNG entries, or a 1-bit mask in old icons.
Metadata: the BMP can carry nothing beyond the header's resolution fields (and a colour profile in rare V5 headers); ICO can carry only a directory of the sizes inside, with no EXIF, but nothing is copied across.
About BMP
BMP stores raw, uncompressed pixels. Files are huge but trivially simple, which is why some legacy Windows software, embedded displays and printers still ask for it.
A BMP is a 14-byte file header ('BM' and the offset to the pixels), a DIB header (40 bytes, or 108 and 124 bytes in the V4 and V5 versions that add colour masks and alpha), an optional palette, then pixel rows padded to 4 bytes and normally stored bottom-up.
BMP files usually come from Windows Paint, legacy Windows programs, embedded displays and some scanners.
About ICO
ICO is a container that bundles several sizes of the same icon (16, 32, 48, 256 px) into one file. It is still the most compatible format for website favicons and Windows app icons.
An ICO starts with a 6-byte ICONDIR (type 1 for icons) and a 16-byte entry per image giving width, height, colour count and offset. Each image is either a BMP without its file header plus an AND mask, or a complete PNG.
When converting BMP to ICO makes sense
ICO is the better choice for favicons and Windows icons, while BMP suits legacy software and embedded systems that require it.
ICO strengths: Multiple sizes in one file; Required by Windows and supported by every browser as a favicon. Drawbacks to weigh: Max 256×256 per image; Not for photos.
Limitations
- BMP stores nearly every pixel literally, so almost any compressed target is several times smaller.
- A 32-bit BMP can carry an alpha byte that most programs ignore; if the image suddenly gains transparent areas after converting, that byte was set.
- Each size inside the ICO is scaled from your image, and detailed artwork loses legibility at 16 and 32 px, so simplify logos first.
- Non-square images are centred on a transparent square for each icon size.
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Frequently asked questions
Does converting BMP to ICO lose quality?
ICO is written losslessly, so the pixels are stored exactly as decoded.
Is transparency kept in the ICO?
Yes. BMP stores it as an optional fourth byte in 32-bit files, which many programs ignore, and the ICO is written with an alpha channel, so transparent areas stay transparent.
Which icon sizes are included?
16, 32, 48 and 256 px by default, the set Windows and browsers expect. You can choose other sizes. Non-square images are centred on a transparent square.
Which apps open ICO files?
Every browser (as a favicon), Windows and most Linux desktops.
Are my images uploaded anywhere?
No. Processing happens inside your browser with WebAssembly and Web Workers. The site only downloads the app code and codecs; your files never leave your device. You can confirm this with the live upload counter on the tool, or in your browser's network panel.
Can I process many files at once?
Yes. Drop a whole selection or folder. Files are processed in parallel on several worker threads, each result can be downloaded on its own, and everything can be saved as one ZIP.
Is it free? Is there a file limit or watermark?
It is free with no account, no watermark and no daily limit. The only limit is your device's memory: very large images (over roughly 100 megapixels) may be refused to keep the tab from crashing.