Glossary
What Is a BMP File?
A BMP file is a bitmap image, a Windows format that stores the color of every pixel directly with no compression. That keeps the picture exact and lossless, but it also makes BMP files far larger than JPG or PNG, so they are mainly used for simple graphics and temporary work rather than long-term storage or the web.
TL;DRBMP is an uncompressed Windows bitmap, exact but heavy. Convert it to JPG or PNG to make the file small enough to share.
~36 MB
the size of one uncompressed 12-megapixel photo saved as a 24-bit BMP, against a few MB as JPG
Why BMP Files Are So Large
A BMP records each pixel on its own. A 24-bit image spends three bytes on every single dot, and nothing is squeezed out afterward. Multiply that by millions of pixels and the file balloons. JPG and PNG, by contrast, compress the data, which is why the same picture shrinks to a fraction of the size once converted.
BMP does have an optional run-length encoding mode, but it only helps flat areas of solid color and is rarely used. In practice almost every BMP you meet is fully uncompressed.
When BMP Makes Sense, and When to Convert
BMP is fine for a quick screenshot, a simple icon, or pixel data handed between Windows programs that expect it. It is the wrong choice for anything you store, email, or put on a website, where the bulk becomes a problem.
Most websites and many image galleries reject BMP uploads outright, both for the file size and for patchy browser support. Convert to JPG or PNG before sharing.
How to Convert a BMP File
A batch converter turns a folder of BMP images into compact JPG or PNG files in one pass, so the pictures keep their look but lose the weight.
Related Guides
Related Terms