The short answer
For any modern use, WebP wins over BMP without contest. BMP is an uncompressed (or barely compressed) bitmap format from 1986, storing each pixel literally. A BMP file is often 10–50× larger than the same image as WebP. BMP has no place in web delivery. Its only remaining merits are simplicity and exactness for niche local workflows.
If you have BMP files destined for the web, convert them to WebP. There is no scenario where serving BMP online is the right choice.
What each format is for
BMP (Windows Bitmap) was introduced by Microsoft in 1986 to store raster images in a simple, uncompressed layout that any program could read and write trivially. Each pixel is recorded directly, with no compression in the common case. That simplicity was its purpose.
WebP, released by Google in 2010, was built for the opposite priority: the smallest possible files for web delivery, using lossy and lossless compression. The two formats sit at opposite ends of the size-versus-simplicity spectrum. See the WebP format overview and BMP format overview.
Where WebP wins
File size
WebP is dramatically smaller than BMP — typically by one to two orders of magnitude. A 1920×1080 photo is around 6 MB as an uncompressed 24-bit BMP and 100–200 KB as lossy WebP. For web delivery, BMP's size is disqualifying on its own.
Transparency and animation
WebP supports an 8-bit alpha channel and animation. Classic BMP supports neither in practice — transparency is effectively unavailable and it is single-frame only. WebP covers use cases BMP cannot represent at all.
Web suitability
WebP is engineered for the web: correct MIME type, <picture> fallback, CDN negotiation, and CMS support. BMP is a local desktop format with none of this infrastructure. Browsers can display BMP, but no one should serve it.
Where BMP wins
Simplicity
BMP's uncompressed layout is trivially simple to parse and generate. Reading a BMP requires no decoder library — the pixels are right there. For a quick-and-dirty local tool or a hardware target with minimal code, that simplicity has value.
Exact, decoder-free pixels
Because BMP stores pixels literally with no compression step, there is no codec to trust and no decode cost. For certain scientific, embedded, or legacy workflows that want raw pixels on disk, BMP is predictable. WebP's lossless mode achieves the same fidelity far smaller, but requires a decoder.
File size in real numbers
The size gap is the whole story. Holding a 1920×1080 24-bit image constant:
- BMP (uncompressed) ≈ 6 MB
- WebP lossless ≈ 1–2 MB
- WebP lossy q=80 ≈ 100–200 KB
For a logo or screenshot with flat colour, WebP lossless can be 50× smaller than the BMP while remaining bit-perfect.
Recommendation
Use WebP for anything on the web, and for any case where file size matters at all. Use BMP only for local workflows that genuinely need decoder-free, uncompressed pixels — and even then, WebP lossless is usually the better choice.
If you have BMP files to publish, convert them to WebP first. Serving BMP online wastes bandwidth for no benefit.
Further reading
- What is WebP? A Complete Guide to the WebP Image Format — the complete format overview
- BMP format overview — the uncompressed bitmap in detail
- Lossy vs Lossless Compression: When to Use Each for WebP — choosing a WebP mode
- PNG vs JPG vs WebP vs AVIF: The Complete Web Image Format Guide — the web format landscape
- Convert images: PNG to WebP, JPG to WebP