Image formatsince 1985

.ico — Microsoft Icon

A multi-size icon container used for favicons, Windows shortcuts, and desktop apps.

Extensions
.ico
MIME
image/x-icon, image/vnd.microsoft.icon
Standard
Microsoft Windows icon container
Released
1985

About this format

ICO is not just a single bitmap. It is a container that can hold multiple icon images at different sizes and bit depths, often including PNG-compressed entries for larger icons.

That is why favicons still commonly use .ico: one file can include 16 px, 32 px, 48 px, and 256 px versions, letting browsers and operating systems choose the right representation.

Real-world samples & file sizes

Four real ICO files downloaded from an external sample library. ICO is a container format: one .ico file often stores multiple sizes so browsers and operating systems can pick the best icon.

Coffee Icon sample preview at 128, 64, 48, 32, 16
Multi-size icon128, 64, 48, 32, 16

Coffee Icon

An ICO container with several embedded icon sizes.

55 KB ico.ico ↓
ConvertICO sample files · Free sample file
Colors Icon sample preview at 64, 32, 16
64 px icon64, 32, 16

Colors Icon

A smaller favicon-style ICO sample.

7 KB ico.ico ↓
ConvertICO sample files · Free sample file
Funky Cluck sample preview at 48, 40, 32, 24, 20, 16
48 px icon48, 40, 32, 24, 20, 16

Funky Cluck

A classic Windows icon container with several small bitmap entries.

25 KB ico.ico ↓
ConvertICO sample files · Free sample file
ICO Sample sample preview at 256, 128, 64, 48, 32, 24, 16
256 px icon256, 128, 64, 48, 32, 24, 16

ICO Sample

A larger ICO container that includes a 256 px PNG-compressed entry.

116 KB ico.ico ↓
ConvertICO sample files · Free sample file

Attribution metadata is mirrored in public/samples/ico/attribution.json.

Pros

  • +Can store multiple icon sizes in one file
  • +Still widely supported for browser favicons
  • +Works well for Windows desktop shortcuts
  • +Can contain PNG-compressed high-resolution icon entries

Cons

  • −Awkward to edit compared with PNG or SVG
  • −Not useful for photos or regular web images
  • −Metadata and embedded sizes are not obvious from the extension
  • −Modern app icon workflows often prefer SVG or PNG source assets

Where it works

Operating systems
  • Windows ✅
  • macOS ✅ for preview/use
  • Linux ✅
Browsers
  • Chrome ✅
  • Firefox ✅
  • Edge ✅
  • Safari ✅
Apps
  • Windows Explorer ✅
  • Browser favicon loaders ✅
  • Figma ⚠️
  • ImageMagick ✅

Related tools

Frequently asked questions

Why does one ICO file contain multiple sizes?
Operating systems and browsers need icons at different scales. ICO stores several images in one file so the viewer can pick the best size.
Should I use ICO or SVG for a favicon?
Use ICO when you need broad legacy favicon compatibility. Use SVG or PNG alongside it for modern browsers and high-density displays.

Other image formats