Why a logo ends up as WebP
WebP is what you get when you right-click and save a logo from most modern websites. Content delivery networks convert uploads to WebP automatically, so even a logo that was originally a PNG is served as WebP to a Chrome or Firefox visitor. The format supports both lossy and lossless compression and an alpha channel in either mode, which means a saved WebP logo may or may not have a transparent background depending on how the site encoded it.
Why not just use the WebP as the favicon
Technically most current browsers will accept a WebP in a link rel icon tag. In practice the .ico route is still the reliable choice: Windows will not use WebP for shortcut icons, some bookmark syncing services and older embedded browsers ignore unknown icon types, and every browser knows to try favicon.ico at the site root without any HTML at all. ICO is the lowest common denominator, and this converter builds a modern one.
What the conversion does with your WebP
The browser decodes the WebP natively, so both lossy and lossless variants work and alpha is preserved. The image is drawn to a square canvas at 16, 32, 48, 64 and 256 pixels, each square is saved as a PNG, and the five PNGs are written into one .ico container. Transparent pixels remain transparent in every entry. If the WebP was lossy, its compression artifacts are baked in; they are usually milder than JPEG artifacts at similar file sizes, but a heavily compressed WebP will still show soft, slightly noisy edges once scaled down.
Animated WebP is decoded as a still: only the first frame is drawn, exactly as with a GIF source. Animated favicons are not something ICO supports anyway.
Sizes and how browsers choose between them
When a favicon file contains several images, the browser reads the directory and picks the entry closest to the size it needs, then scales that one. Chrome on a standard display asks for 16 pixels for the tab and 32 for the bookmarks bar; on a high resolution display it doubles those numbers, so the 32 and 64 entries get used. Windows Explorer prefers 48 for medium icons and 256 for extra large views. Supplying all five means every consumer finds a near match, and the quality of the small ones depends on the source being clean and square.
Realistic file sizes
A 400 by 400 lossless WebP logo of 18 KB typically becomes an ICO of 25 to 40 KB, since PNG entries are a little larger than lossless WebP for the same pixels. A lossy 40 KB WebP of a photographic badge may produce a 100 KB ICO because PNG cannot compress photo textures well. These are typical outcomes; the exact number depends entirely on the artwork. The size of the .ico is not a performance concern for a favicon, browsers cache it aggressively.
Things to check before you convert
Make the image square first, because the canvas stretches non-square input rather than padding it; the crop tool handles that in seconds. Confirm whether the background is actually transparent by opening the WebP over a dark page; many saved logos have a white box baked in. If it does, remove it with the background remover before converting. Finally, if the logo you saved is not yours, check that you are allowed to use it. The conversion itself runs entirely on your device and nothing is uploaded.