What is BMP and why is it so large?
BMP (Bitmap) is one of the oldest image formats, developed by Microsoft and built into Windows from its earliest days. Unlike JPEG or PNG, BMP files are almost entirely uncompressed — every pixel is stored as raw colour data. A 1920×1080 screenshot in BMP is around 6 MB, while the same image as a JPEG at quality 85 is under 400 KB. BMP files come from older Windows applications, screen-capture tools that default to BMP, legacy industrial or medical imaging software, and some paint programs on older operating systems.
Converting BMP to JPG dramatically reduces file size without visible quality loss on screen. JPG is also universally accepted everywhere BMP is not — web upload forms, email clients, and photo-sharing platforms expect JPEG, not BMP.
Convert BMP to JPG without uploading
LocalJPG converts BMP files entirely in your browser using the createImageBitmap and OffscreenCanvas APIs built into modern browsers. The BMP is decoded on your device and re-encoded as JPEG via MozJPEG. Nothing is transmitted — the file never reaches any server.
This matters for BMP exports from industrial software, scanned documents from legacy systems, or screenshots containing sensitive data. You can verify no upload occurs by watching the Network tab in DevTools while converting — zero outbound image requests appear.
How much smaller does JPG get vs BMP?
The size reduction is dramatic. A typical 1920×1080 BMP screenshot is 5–6 MB. The same image as a JPEG at quality 85 is 150–400 KB — a 10–30× reduction with no visible quality loss on screen. For photos with complex detail, JPEG quality 85 is essentially indistinguishable from the uncompressed BMP to the human eye.
If you need a specific target size (for upload forms with strict limits), use the built-in resize tool: set a maximum in kilobytes and LocalJPG will adjust JPEG quality automatically.
Batch converting BMP files
Drop a folder of BMP images and the converter processes them in parallel in a background Web Worker. Because BMP files are large, the browser decompresses them quickly with no upload latency. Download the JPGs one at a time or grab them all as a single ZIP, assembled entirely in-browser — both free.
Also available: HEIC to JPG, WebP to JPG, PNG to JPG, TIFF to JPG