Why does my favicon look blurry on a Retina or 4K display?

Browsers pick the entry closest to the requested device-pixel size. If your favicon.ico contains only a 16x16 entry, a Retina MacBook tab (which actually renders the favicon at 32x32 physical pixels) upscales that 16x16 by 2x — producing visible blur. Add at least a 32x32 entry, and ideally 48x48, so the browser has a sharper source for high-DPI scaling.

Should I include a 256x256 entry in my favicon.ico?

Probably not. 256x256 is intended for Windows Explorer "Extra Large Icons" view and Windows app icons, not browser favicons. Including it in your site's /favicon.ico adds 5-30 KB to a file requested on nearly every page load. Modern best practice: ship 16/32/48 in the ICO and serve 180x180 (Apple) and 192x192/512x512 (Android/PWA) as separate PNG files declared in your HTML head and Web App Manifest.

Will upscaling a small ICO to a larger size look good?

No. ICO entries are bitmaps — upscaling a 16x16 entry to 64x64 produces blocky, jagged edges no matter what resampling algorithm the resizer uses. Always work from the largest source you have (ideally a 256x256 or 512x512 PNG, or better, a vector SVG/AI master) and downscale to each target size. If you only have a 16x16 ICO, redraw the icon at a larger size before resizing — the upscale path can't recover detail that was never captured.

Can one ICO file really hold multiple sizes?

Yes — that's the format's defining feature. The ICO header is a directory with one entry per embedded image, and the file can technically contain up to 65,535 entries (the IDCount field is a 16-bit unsigned integer). In practice, favicon.ico files hold 3-6 entries (16/32/48 plus optional 64 and 96) and Windows app ICOs hold 6-9 entries (16/24/32/48/64/128/256). Browsers and the OS automatically pick whichever embedded size is closest to the display target.

Does resizing preserve transparency?

Yes, as long as the source ICO uses 32-bit RGBA (the standard since Windows XP). Each resized entry keeps the alpha channel. If your source is an older 24-bit ICO with a 1-bit AND-mask, edges may show a colored fringe after downscaling — the workaround is to convert the master to 32-bit RGBA first, then resize.

What's the maximum size an ICO can store?

256x256 pixels. The width and height fields in the ICO directory entry are single bytes, with the value 0 used to represent 256 (since 256 itself doesn't fit in 8 bits). For anything above 256x256 — Android 512x512 icons, PWA splash screens, macOS app icons at 1024x1024 — you need PNG or ICNS, not ICO.

Can I add a brand-new size to an existing ICO?

Not directly — you need to rebuild the ICO with the new entry. Upload your existing ICO here, pick Preset Resolutions or By Width & Height for the new size, and download. For a fresh multi-size ICO built from a single high-resolution source, start with a 256x256 or larger PNG master and convert it via PNG to ICO, which packs the standard 16/32/48 entries automatically.

How small can a favicon.ico get?

A well-built 16+32+48 favicon.ico with 8-bit indexed entries for the 16x16 and 32-bit RGBA for the 48x48 typically lands at 4-6 KB. PNG-compressed 32-bit entries can push it under 4 KB. If you're seeing 30 KB+, the file likely contains unnecessary 128x128 or 256x256 entries, or every size is stored as uncompressed 32-bit BMP — both fixable by resizing here and keeping only the sizes you actually need.

What if I just need a single-size PNG instead of an ICO?

Use ICO to PNG to extract the largest entry as a PNG (handy for design tools that don't read ICO), or Compress ICO if your goal is shrinking an existing multi-size file. Crop ICO is useful when the source icon has whitespace padding you'd like to trim before downscaling to 16x16.

Resize ICO

Resize ICO icon files to any dimension. Create favicons at 16×16, 32×32, 48×48, 64×64, or custom sizes with quality preservation.

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