Convert ICO icons for free, and see how one file holds several sizes, all in your browser.
One .ico holds many images, and something else decides which one you see
An icon file is a 6-byte header and a directory of 16-byte entries, each pointing to either a headerless BMP (with its height doubled to make room for a 1-bit AND mask) or, since Windows Vista, a complete PNG. Width and height are single bytes, so 256 is written as 0. A .cur is the same file with a hotspot instead of colour-plane fields. Open one, or the samples built here, and see every entry decoded by this page and the one your browser actually picks.
app.ico: Windows-style: 16, 24, 32, 48 as 32-bit BMP with AND masks, 256 as PNG (written as 0)For an img element without a size, the browser chooses one entry as the image’s natural size: entry 4 (PNG, 256 px), pixel-matched against this page’s decode with max difference 0. createImageBitmap gave 256 × 256.
Small sizes compress badly as PNG and are often smaller as BMP; 256 px is huge as BMP (262 KB with mask) and tiny as PNG. Windows wants 16, 24, 32, 48 and 256; browsers mostly use 16 and 32. Drop an image or use the generated one, toggle each size, and the file is written and read back by the inspector above.
Add your ICO icon file, choose PNG as the output, and convert. PNG keeps the transparency and sharp edges of the icon and opens in any image editor or viewer, which makes it easy to reuse the graphic outside of a Windows icon context.
Yes. You can convert ICO to common formats such as PNG and JPG. PNG is the best choice because it preserves the icon transparency, while JPG produces a smaller file without an alpha channel.
Yes, it is free with no account, no watermark, and no limit. You can convert as many icon files as you need directly in your browser, with nothing to install.
Yes, when you convert to a format with an alpha channel such as PNG. Icons often have transparent backgrounds, and PNG preserves that. Converting to JPG will fill transparent areas because JPG does not support transparency.