ICO to JPG
Nothing you choose here leaves your browser, and nothing is downloaded to make it work. An ICO usually holds several images, so this shows what is actually inside and lets you choose.
The same, when something insists on a JPG.
Icons are transparent and JPGs are not, so the transparency is flattened onto a colour you choose. For anything else PNG is the better answer — it is lossless, it keeps the transparency, and an icon is small enough that the file size argument for JPG does not apply.
An ICO holds several sizes, and that is the whole point
Most converters write one image into an icon file and stop.
That is a legal ICO and a worse one than the format allows. An
.ico is a container: it holds a set of
pictures, and whatever displays it picks the one that fits the space
— 16 pixels in a browser tab, 32 on a taskbar, 48 on a Windows
desktop, 256 in a large icon view.
That matters because an icon drawn for 16 pixels is not a shrunken 256-pixel one. Detail that reads beautifully at full size turns to mush at tab size. Including the small entries means the browser uses one made at that size rather than squashing the big one itself.
What is written, and why it is two different things
Sizes up to 64 pixels are written as Windows bitmaps, which every version of Windows has understood since 1985 — a favicon has to work in old software. 128 and 256 are written as PNG, because an uncompressed 256-pixel bitmap is about a quarter of a megabyte and the PNG is a fraction of that. PNG inside an ICO was added to the format for exactly this reason.
Your browser cannot write an ICO at all — asking a canvas for one silently returns a PNG, which is the sort of thing this site checks for — so the container is written here. Nothing is fetched to do it.
What it will not do
It will not make a small icon good. At 16 pixels almost nothing survives but a silhouette, and a logo with words in it will not be readable at that size in any icon, from any tool. That is the size, not the conversion, and no converter can fix it — the answer is a simplified mark drawn for small sizes.
It does not crop. A picture that is not square is squashed to fit rather
than trimmed, because trimming would decide for you which part matters.
It also does not read .icns, which is Apple's icon format
and a different thing entirely — ICNS to JPG
is the page for that — or animated cursors.
Where to go next
- JPG to ICO — the same conversion the other way
- PNG to ICO — another way in
- WebP to ICO — another way in