FormatDrop
Image Format

ICO

Windows Icon

ICO is the format behind every favicon, every Windows application icon, and every taskbar icon. It's a container that holds multiple image sizes in one file, allowing Windows and browsers to pick the right size for the context. Here's everything you need to know about ICO and how to create favicon.ico files from PNG or SVG.

What is ICO?

ICO (Windows Icon) is a file format developed by Microsoft for storing application icons in the Windows operating system. Unlike single-resolution image formats, an ICO file is a container that holds multiple images at different sizes and colour depths — typically including 16×16, 32×32, 48×48, and 256×256 pixel versions of the same icon. Windows picks the appropriate size from the container depending on where the icon is displayed: 16×16 for taskbar and file explorer list view, 32×32 for desktop icons and file explorer medium view, 48×48 for large icon view, and 256×256 for extra-large view and higher-DPI displays. Images inside an ICO file can use BMP (bitmap) encoding at various colour depths or PNG encoding (supported since Windows Vista and Windows 7). ICO became the standard format for web favicons — the small icons shown in browser tabs, bookmarks, and address bars — through an HTML link tag: `<link rel="icon" href="/favicon.ico">`. Browsers still request favicon.ico from the root of a website by default even without the link tag, which is why favicon.ico at the website root is conventional. Modern web development has moved beyond ICO for favicons: the Web App Manifest and PNG favicons at specific sizes (16×16, 32×32, 180×180 for Apple touch icon, 192×192 for Android) are now the standard for full favicon support. But favicon.ico remains necessary for backward compatibility with older browsers, RSS readers, and some email clients that display site favicons.

ICO pros and cons

Advantages

  • Multi-resolution container — one file holds 16×16 through 256×256 versions
  • Windows picks the optimal size for each display context
  • Universal browser favicon support (all browsers request favicon.ico)
  • Required for Windows desktop application icons
  • PNG images inside ICO support transparency

Limitations

  • ICO is Windows-specific — not used on macOS (uses ICNS) or Linux
  • Limited to icons — not suitable for general image storage
  • Creating ICO files requires specific tools (most standard image editors don't save ICO)
  • Modern favicons use PNG + Web App Manifest instead of ICO for better quality
  • 256×256 PNG-inside-ICO is the maximum — not suitable for high-DPI displays above 2×

When should you convert ICO files?

Convert PNG to ICO when you're creating a website favicon (start with a 512×512 or larger PNG of your logo, convert to ICO at 32×32 and 16×16 sizes), building a Windows desktop application (Windows requires ICO for app icons), or customizing folder icons in Windows (Windows accepts ICO for custom folder icons). Convert JPG or SVG to ICO via PNG as an intermediary — export as PNG first, then convert PNG to ICO.

Convert ICO files

PNG→ICO
JPG→ICO

All FormatDrop conversions run entirely in your browser — no file upload, no server processing. Your files stay on your device.

ICO FAQ

How do I create a favicon.ico for my website?
Start with your logo or icon image as a square PNG at 512×512 pixels or larger. Convert to ICO using FormatDrop — the converter generates a multi-size ICO containing 16×16 and 32×32 pixel versions. Place the resulting favicon.ico at the root of your website (https://yoursite.com/favicon.ico). Add a link tag in your HTML head: `<link rel="icon" href="/favicon.ico" sizes="any">`. Also add a PNG favicon for modern browsers: `<link rel="icon" href="/icon.png" type="image/png">`.
What size should a favicon.ico be?
A favicon.ico should ideally contain multiple sizes: 16×16 (browser tab), 32×32 (taskbar and search results), 48×48 (Windows desktop), and 256×256 (high-DPI contexts). Most favicon generators create all of these from a single source image. The source image should be at least 512×512 pixels for the best quality at all sizes.
Is ICO or PNG better for favicons?
Modern practice uses both: an ICO file for broad compatibility (especially with old IE, RSS readers, and non-browser tools) plus PNG files at specific sizes (16×16, 32×32, 192×192 for Android, 180×180 for Apple Touch Icon) for modern browsers. The HTML link tag lets you specify both: ICO as the fallback and PNG as the preferred format. Browsers use the PNG when supported and fall back to ICO when not.

More formats

HEICWebPAVIFEPUBWebMOpusMP3WAVM4AFLACAACMP4AVIMKVMOVJPGPNGGIFSVGTIFFBMPEPSARWOGGWMVPPTXPagesPDFDOCXRAWHEVCH.264AIFFM4VWMA3GPDNGRTFPSDOGVTSFLVAIXLSXCSVZIPAPNGMIDIJPEG XLMPG/MPEGVOBM2TSAC3ALACDTSJP2HEIFAPECBZ3G2SRTDOCPPTXLSODTODSM3URAR7ZM4BAMRTXTMOBITARGZJSONXMLYAMLKEYMTSCR2NEFMXFTGACAFASSVTTDSFRMF4VWVASFRMVBORFRW2EAC-3TTAISODMGXZDjVuFB2AUM4RAZW3MKAEXRVCFICSAAXPRCMP2SPXXSPFM3U8