Convert BMP to WebP — Free, Fast & Private
Of all the conversions on this site, this one produces the most dramatic numbers, and for a simple reason: BMP does not compress at all. A Windows bitmap is essentially a header followed by the raw pixel values, one after another. Nothing is predicted, nothing is modelled, nothing is squeezed.
The arithmetic is easy to do in your head. A 1920 × 1080 image at 24 bits per pixel is 1920 × 1080 × 3 bytes — about 5.9 MB — and it is that size whether it shows a detailed photograph or a plain white rectangle. The same image as WebP might be 150 KB. That is a 97% reduction, and it is typical rather than exceptional.
Where BMP files still come from
Mostly from Windows software that has not been rethought in a long time. Older versions of Paint default to BMP. A great deal of scientific and industrial equipment — microscopes, machine-vision cameras, medical instruments, test rigs — writes BMP because it is trivially simple to implement and has no licensing questions attached. Some screen-capture utilities and legacy line-of-business applications still produce it too.
The result is that people usually meet BMP as a problem: a folder of enormous files that will not attach to an email, will not upload to a form, and fills a drive far faster than it should.
You are not losing anything you had
This is the important reassurance, and it is genuinely different from most lossy conversions. A BMP is normally the first encoding of the image — the raw output of a capture — not a file that has already been through a lossy codec. So converting to WebP is a single, first-generation lossy pass on pristine data, which is the best possible case for any codec. The artefacts that make people wary of lossy compression come mostly from stacking generations, and there is no stack here.
If the image is a screenshot, a diagram or line art rather than a photograph, use a high quality setting or convert to PNG instead. PNG is lossless, still compresses BMP by an enormous margin, and keeps text edges perfectly sharp — sharp edges being precisely what lossy codecs soften first.
Transparency is worth a note. Most BMP files are 24-bit with no alpha channel, though a 32-bit BMP can carry one. Where alpha is present, WebP preserves it; where it is absent, nothing is invented.
Converting a large batch
BMP problems arrive in bulk — a whole capture session, a whole instrument export. Feed them in 5 at a time on the free tier, or drop the entire folder at once on Pro, which removes the batch cap; either way you can download everything as a single ZIP. Because the conversion runs in your browser rather than on a server, a large batch is not throttled by an upload, which is exactly the bottleneck that makes BMP painful with cloud converters.
That local processing also matters if the images are instrument data, medical captures or anything else you would rather not post to a third party. For maximum compatibility instead of minimum size, BMP to JPG opens anywhere; for the smallest files of all, BMP to AVIF.