ICO (Windows Icon)
ICO is the Windows icon container, and the traditional format for a website’s favicon.
- File extension
- .ico
- MIME type
- image/x-icon
- Compression
- Lossless
- Transparency
- Yes, full alpha channel
- Animation
- No
- Type
- Raster (pixels)
Where ICO files come from
Website favicons and Windows application icons.
Universal for its one job: favicons and Windows icons.
What ICO is good at
- Holds several sizes in one file so each context picks the sharpest
- The one favicon format every browser understands, including very old ones
- Supports transparency
Where ICO falls short
- Only useful for icons — sizes are capped at 256x256
- Not a general-purpose image format
- Awkward to create in most image editors
Should you use ICO?
Use it when the image must survive editing and re-saving without degrading, or when transparency matters. Avoid it for large photographs that only need to be viewed, where a lossy format will be a fraction of the size with no visible difference.
Frequently asked questions
What is ICO (Windows Icon)?
ICO is the Windows icon container, and the traditional format for a website’s favicon. Universal for its one job: favicons and Windows icons.
How do I open ICO files?
Any tool that lists ICO support will open one. If yours will not, the quickest fix is to convert it to a format your software already understands — the converters linked on this page do that in your browser without uploading the file.
Is ICO lossy or lossless?
ICO is lossless — every pixel is stored exactly, and re-saving it repeatedly costs you nothing in quality. The trade-off is a larger file.
Does ICO support transparency?
Yes, ICO carries a full alpha channel, so soft edges and drop shadows survive intact. Converting to a format without alpha — JPG most commonly — flattens those areas onto a solid colour.