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ICO converter

An .ico file is a Windows icon container that bundles the same artwork at several sizes and color depths so the OS can pick the best match for any context. On the web it survives as the classic favicon format, with favicon.ico still the fallback path every browser requests.

Private for supported formats — processed in your browser

Convert supported files

Runs on your device

Drop ICO files here

Batch files can each use a different output. Nothing uploads for local conversions.

Working inputs include camera RAW, browser-local audio/video, PDF, CBZ/CBR comics, office documents, ebooks, markup, 3D models, structured text, images, and archives.

Where ICO comes from

Icons shipped with Windows 1.0 in 1985 as monochrome 32x32 bitmaps and grew color and multiple resolutions across later releases. Internet Explorer 5 introduced the favicon convention in 1999, and Windows Vista (2006) extended the container to accept PNG-compressed entries for 256x256 icons.

How ICO works

  • A directory header indexes multiple images, each with its own dimensions and bit depth
  • Entries are either uncompressed BMP data (headerless DIBs with an AND transparency mask) or complete embedded PNGs
  • Maximum entry size is 256x256 pixels
  • The sibling .cur cursor format shares the same structure plus a hotspot coordinate
  • Windows selects among the bundled sizes (16, 32, 48, 256...) depending on display scale and context

When to use ICO

  • Website favicons served from the /favicon.ico fallback path
  • Application and shortcut icons for Windows executables
  • Taskbar, tray, and file-association artwork at multiple resolutions

Strengths and limitations

Strengths

  • Multiple resolutions in a single file, chosen automatically
  • Understood by every browser and every version of Windows
  • PNG entries keep even the 256-pixel size compact

Limitations

  • Hard 256x256 ceiling makes it useless for general imagery
  • The legacy BMP-plus-mask entry format is fiddly to author correctly
  • Modern web manifests favor plain PNG and SVG icons, shrinking its role

Compatibility

All browsers request and render .ico favicons, and Windows depends on the format throughout its shell. macOS and Linux open it via common image libraries but use their own native icon formats (.icns, themed PNGs), so .ico matters chiefly for Windows software and website roots.

Convert ICO to another format

Convert other formats to ICO