BMP to WebP Converter

BMP files are uncompressed, so screenshots, scans and diagrams saved as bitmaps waste a lot of space. WebP shrinks them dramatically and is supported by every current browser and most image software. This converter decodes each BMP in your browser and saves a WebP — lossless by default, which keeps every pixel of screenshots and graphics, or lossy with a quality setting for photos — and shows how much each file shrank.

How to use this tool

1. Drop one or more .bmp files.
2. Keep lossless on for screenshots, text, diagrams and pixel art; turn it off for photos and set the quality.
3. Optionally set a max size; choose "Always libwebp" for the smallest lossless files.
4. Convert, check the size change and download the WebP files.

Formula

Size change = (WebP bytes ÷ BMP bytes − 1) × 100%. A 24-bit BMP takes 54 bytes + height × (width × 3, rounded up to a multiple of 4).

Lossless WebP (VP8L) stores the exact pixels using prediction, colour caching and entropy coding; flat-coloured screenshots usually shrink by far more than 90%. Lossy WebP (VP8) suits photos. Chrome, Edge and Firefox encode WebP themselves; Safari cannot, so there the page loads libwebp compiled to WebAssembly (about 30 MB, once). Transparency of 32-bit BMPs is kept.

Example

A 1920 × 1080 24-bit screenshot.bmp is 54 + 1080 × 5,760 = 6,220,854 bytes. If the lossless WebP comes out at 311,043 bytes, the size change is 311,043 ÷ 6,220,854 − 1 = −95.0%, shown under the file; the exact saving depends on the picture.