How to Convert TIFF to ICO in Your Browser

How TIFF becomes ICO

1. The browser's TIFF decoder reads the file's byte-order header (little-endian 'II' or big-endian 'MM') and unpacks only the first page — the first IFD — into raw RGBA pixel data; any additional pages in a multi-page TIFF are never touched.
2. That first page is resized to each icon resolution, typically 16, 32, 48, and 256 pixels, carrying its alpha channel through if the source has one.
3. Each resized version is PNG-compressed and written into the ICO's ICONDIR as its own entry, producing one file containing every resolution.

What changes when you convert

TIFF-to-ICO is an unusual pairing, since TIFF is normally an archival or print format rather than something people think of as icon source material. A real practical case is a multi-page scanned document: converting its first page into an ICO gives that specific file a distinctive thumbnail-style icon, rather than the generic document icon your OS would otherwise show.

Because only the first page converts, a multi-page TIFF's later pages are simply unavailable to this tool — there's no way to select page two of a scanned contract and turn that into the icon instead. If the page you actually want isn't page one, you'd need to split or re-export it as its own file first.

TIFF can carry a genuine alpha channel, and when the source has one, it's preserved through to the icon's PNG frames the same as any other source with real per-pixel transparency. Plenty of TIFF files — especially scans — have no alpha at all, in which case the icon is simply opaque.

When ICO is the right choice — and when it isn't

ICO exists to give Windows a single file containing an icon at every size the OS needs, from a 16px title-bar icon up to a 256px high-DPI shortcut. If the first page of a TIFF is destined to become an app icon, desktop shortcut, or favicon, that's exactly the job ICO does.

TIFF's own reason for existing is archival fidelity — raw, essentially uncompressed pixel data suited to print production and long-term storage — and none of that fidelity matters to an icon, which tops out at 256 pixels and is always PNG-compressed. Converting to ICO only makes sense once you've decided the output's job is to be a small Windows icon, not a preservation copy; if you need a smaller, shareable version of a TIFF that keeps its full resolution, converting to WebP or AVIF serves that goal far better than ICO does.

Limitations and privacy

Only the first page of a multi-page TIFF is ever used — later pages aren't extracted, previewed, or offered as an alternative. Large, high-resolution TIFF files can also take longer to decode in the browser than more compact formats before conversion even begins.

Decoding the first page, resizing it, and packaging into the ICO container all happen locally in your browser. The file is never uploaded to a server for this workflow.