BMP is an old, uncompressed format that stores every pixel with no compression whatsoever. A BMP file of a modest photograph can easily reach 5–10MB. The same image as a JPG is typically 200–500KB — a reduction of 90% or more with no visible quality difference at normal viewing sizes. For anything beyond local archiving on a Windows machine, BMP is the wrong format, and converting to JPG is the standard fix.
Portimg's image converter handles BMP to JPG in the browser without any software to install.
Why BMP files are so large
Unlike JPG, which analyses an image and discards data the human eye is unlikely to notice, BMP stores every pixel's colour values in full. A 1920×1080 image in BMP format stores over 2 million pixels with 3 bytes of colour data each — around 6MB just for the raw pixel data, before any file overhead. JPG achieves its compression by grouping similar areas of an image and encoding them more efficiently, which is why the same image can be ten times smaller with no perceptible quality loss at standard settings.
This is also why BMP files have almost no legitimate use on the web or for sharing. They're a Windows legacy format that predates modern compression, and the only reason they still appear is that some older Windows applications create them by default.
Converting with Portimg
Go to portimg.com/raster-to-raster-converter, upload your BMP file or files, select JPG as the output format, and download the result. Batch uploads are supported if you have multiple files. No account is required, and files are deleted from the server after processing.
The conversion from BMP to JPG involves a quality setting — how aggressively the JPG compression is applied. At high quality settings, the output file is larger but retains more detail. At lower quality settings, the file is smaller but may show visible compression artefacts, particularly in areas with fine detail or sharp edges. For most uses — web images, shared photos, documents — a high quality setting produces output that is visually identical to the BMP at a fraction of the size.
Whether JPG is the right target
JPG is the right output for most BMP conversions. It's the most universally compatible format and produces the best file size reduction for photographic content.
If the BMP contains graphics with flat colours, text, or line art — a screenshot, a simple diagram, a logo — PNG may actually be a better output than JPG. JPG compression introduces subtle artefacts at the boundaries between flat colour areas and fine text, which can make graphics look slightly soft or blurry. PNG is lossless and handles these types of images cleanly. For photographs and continuous-tone images, JPG is the right choice; for graphics and illustrations, PNG often produces cleaner results at comparable or smaller file sizes.
For images going onto a website specifically, WebP is worth considering as an alternative to JPG — it produces smaller files at equivalent quality and is supported by all major browsers. Portimg's converter handles BMP to WebP if that's your destination.