Guide
Shrinking BMP bitmaps into small JPG or PNG files
BMP, the Windows bitmap, is one of the oldest image formats still in use. Paint saved to it for decades, industrial cameras and lab instruments still export it, and old games and business software keep generating it. The format is simple, which is its strength, and wasteful, which is its weakness: almost nothing is compressed. Converting BMPs to JPG or PNG typically cuts their size by a factor of ten or more.
How a bitmap is stored
A 24-bit BMP writes every pixel as three bytes, row after row, with a small header in front. There is no clever encoding: a 4000 × 3000 photo needs 36 MB whether it shows a busy street or a white wall. Some BMPs use fewer bits with a color table, a few use simple run-length compression, and 32-bit variants can include transparency. The browser’s decoder reads all the common variants, so this tool accepts them directly.
JPG for photos, PNG for graphics
The right target depends on the content. A scanned photograph or a camera capture becomes a small JPG at 85 to 90 percent quality with no visible change. Screenshots, diagrams, Paint drawings and anything with sharp text should become PNG instead: it is lossless, keeps letters crisp, and for flat-colored images it is often smaller than a JPG would be. You can switch between JPG and PNG in the same tool and compare the sizes in the result rows.
Step by step
Drop the BMP files, pick JPG or PNG and convert. Each row shows the original and new size with the dimensions. Save files one by one or press “Download all” for a .zip. If the bitmaps are larger than needed, for example 4K screen captures for a small manual illustration, switch on “Limit size” and set the longest side in pixels.
Transparent and unusual bitmaps
Most BMPs are opaque, but 32-bit bitmaps from some icon editors and games carry an alpha channel. When you convert those to JPG, transparent areas are filled with the background color you choose. PNG keeps the transparency. Indexed 8-bit bitmaps with 256 colors convert cleanly to both formats; in PNG they stay pixel-identical.
Where this helps
Engineers attach microscope or inspection images to reports and hit email limits. Teachers find old classroom material saved as BMP. Someone cleaning up a legacy Windows application needs its graphics in modern formats. In each case the visual content stays the same while the files become small enough to share, upload or put into documents.
Going the other way
Some legacy software, label printers and microcontroller displays only read BMP. For those, JPG to BMP and PNG to BMP write standard 24-bit or 32-bit bitmaps. For web use, BMP to WebP produces even smaller files than JPG, and the general Image Converter handles everyday formats in any direction.
Checking quality after conversion
Open one converted photo and one converted screenshot at 100 percent zoom. Photos should look the same as the bitmap; if smooth areas show faint blocks, raise the JPG quality to 92 percent. Screenshots saved as PNG should be pixel-identical to the BMP. If a JPG screenshot shows smudged text, convert it again as PNG; that one choice usually matters more than any quality setting.
Checked against the current version of the BMP to JPG on .