How do I create a favicon.ico with ImageMagick?

Use the icon:auto-resize define: magick logo.png -background none -define icon:auto-resize=16,32,48,64,256 favicon.ico. It packs every listed size into one file.

Why does ImageMagick say width or height exceeds limit when writing an ico?

The ICO format caps at 256 by 256 pixels. Converting a larger image directly fails. Use -define icon:auto-resize so ImageMagick downsizes to valid icon dimensions first.

What favicon sizes should I include?

16, 32 and 48 inside the .ico covers browsers and Windows shortcuts. iOS home screen icons at 180 and PWA icons at 192 and 512 must be separate PNG files.

Can a favicon have a transparent background?

Yes. Pass -background none and start from a PNG that already has transparency. The ICO format supports an alpha channel.

ImageMagick favicon and icon set generator

Create a multi-resolution favicon.ico from a PNG with ImageMagick using icon:auto-resize, plus the app icon sizes iOS, Android and PWAs expect.

Multi-resolution favicon.ico

magick logo.png -background none \
  -define icon:auto-resize=16,32,48,64,128,256 favicon.ico

icon:auto-resize packs every listed size into a single .ico file, which is what browsers and Windows both expect. Start from a square source of at least 256×256 — ImageMagick downscales cleanly but cannot invent detail going up.

256 is the ceiling

The ICO format does not support dimensions above 256×256. Listing 512 will either be ignored or produce a file some Windows versions refuse to read. Converting a large image straight to .ico without auto-resize fails outright:

convert: width or height exceeds limit `favicon.ico'

Which sizes do you actually need?

Size	Used by
16×16	Browser tab, bookmarks bar
32×32	Taskbar, high-DPI tab
48×48	Windows desktop shortcut
180×180	iOS home screen (as a PNG, not in the .ico)
192 / 512	Android and PWA manifest (PNG)

16, 32 and 48 inside the .ico covers the browser cases. The larger app icons must be separate PNG files referenced from your HTML or web manifest.

Generate the PNG app icons

for s in 180 192 512; do
  magick logo.png -background none -resize ${s}x${s} \
    -gravity center -extent ${s}x${s} icon-${s}.png
done

Design note: 16×16 is not a small logo

Detailed logos become mud at 16 pixels. If your mark has thin strokes, gradients or text, make a simplified variant — usually a single letter or the boldest shape — and use that for the small sizes:

magick logo-simple.png -background none \
  -define icon:auto-resize=16,32 favicon-small.ico
magick logo.png -background none \
  -define icon:auto-resize=48,64,128,256 favicon-large.ico

Referencing it

<link rel="icon" href="/favicon.ico" sizes="any">
<link rel="icon" href="/icon.svg" type="image/svg+xml">
<link rel="apple-touch-icon" href="/icon-180.png">

Modern browsers prefer the SVG when one is offered, falling back to the .ico. An SVG favicon scales perfectly and is usually smaller than the icon set it replaces.