Favicon Sizes and Multi-Resolution ICO: 16, 32, 48 px and Beyond
16, 32, 48, 64, 128, 256 — the list of icon sizes quickly turns into a soup of numbers. Which ones do you actually need, and which are leftovers from the past? Why does ICO store several resolutions at once, and how many versions is it sensible to pack into one file? Let's go through each size on its merits: where it is used and whether it earns a place in your favicon.
Why there are so many sizes: the multi-resolution idea
An icon is shown in a dozen different places, and each one needs its own size: tiny in a tab, bigger in bookmarks, larger still in the file explorer. You might think you could take one big picture and shrink it as needed. But automatic downscaling kills small icons: thin lines merge, edges turn dirty, text becomes a blob.
The fix is multi-resolution. A single ICO file holds several ready-made versions, each drawn for its own size. That spares the system from shrinking on the fly: it simply grabs the right picture from the set. We cover exactly how this container works in "What Is ICO".
In short
Sizes exist not "just in case" but because a small icon must be drawn separately, simplifying the detail. ICO lets those separate versions live in one file.
Every size and where it lives
To stop guessing, here is a map of sizes and their real uses:
| Size | Where it is used | Needed? |
|---|---|---|
| 16×16 | Browser tab, address bar, history | Required |
| 32×32 | Bookmarks, high-density displays, taskbar | Required |
| 48×48 | Windows file explorer, medium tiles | Recommended |
| 64×64 | Large icons in the explorer | Optional |
| 128×128 | App icons, previews | Optional |
| 256×256 | Large tiles, program icons | For apps |
The takeaway is simple: for a website favicon the key sizes are 16, 32 and 48. Anything bigger belongs to Windows app icons rather than browser tabs.
Which set to put in favicon.ico
The urge to cram every size into the ICO is understandable but harmful: the file bloats with zero benefit. A sensible modern set inside favicon.ico:
The base
Tab and address bar. Non-negotiable — it is the "face" in the tab.
The crisp one
Bookmarks and Retina screens. The browser loves to grab this one.
The large one
Windows file explorer and interface scaling.
These three sizes are enough for the vast majority of sites. Everything else — large PNGs for the apple-touch-icon and manifest — is stored as separate files, not inside the ICO. More on the full set in the "How to Make a Favicon" guide.
Do you need 256×256
The 256×256 size is special: it is the reason ICO was allowed to store a compressed PNG instead of an uncompressed BMP, so the file would not bloat. But do you need it in a favicon?
Usually not. Tabs, bookmarks and history use the small sizes; a large picture simply is not shown there. 256×256 is genuinely needed for app icons and big Windows tiles. If you are building a website favicon, do not drag 256 inside the ICO — instead hand the large resolution off as a separate PNG for the apple-touch-icon and manifest.
The economy rule
Every extra size inside the ICO is weight that loads on every page. For a site, three sizes (16/32/48) are the sweet spot: crisp everywhere with no wasted kilobytes.
Retina, density and apple-touch-icon
On high-density screens (Retina and the like) one logical pixel is made of several physical ones. So on such a screen the browser often grabs the 32×32 version for a "16-pixel" tab — to keep the icon sharp. That is one more reason to keep both 16 and 32 in the ICO: together they cover ordinary and dense displays.
A separate story is the apple-touch-icon. It is not part of the ICO but a standalone PNG that iOS uses for the site icon on the home screen. The modern recommended size is 180×180. People used to make a whole menagerie of sizes for different models, but today a single 180×180 is enough.
How to build a multi-resolution ICO
You don't have to assemble each size by hand. Prepare one large square source and let the converter do the rest:
A 256×256 source
A square PNG with a transparent background and a simplified, readable logo.
Convert to ICO
The converter generates the 16, 32 and 48 versions inside the file.
Check it small
Shrink to 16 px and confirm the silhouette still reads.
Build a multi-resolution ICO
Upload a large PNG and the FormatZ converter packs 16, 32 and 48 into one favicon.ico. Free, in the browser, no sign-up.
Want to do the opposite and break someone's ICO apart into its sizes to see what is inside? The ICO to PNG converter helps. And which format to choose for an icon — ICO, PNG or SVG — is covered in our separate comparison.
