What is a .bmp file?
Bitmap Image File · Image · Microsoft · 1987
BMP is an old, simple Windows image format that stores pixels with little or no compression. Files are large and quality is perfect, which suits some technical uses, but for everyday sharing almost anything else is a better choice.
What is a .bmp file used for?
A BMP is close to raw pixel data plus a small header. Because it barely compresses, files are big, but there is zero quality loss and the format is dead simple for programs to read and write.
It has faded from everyday use because PNG offers the same lossless quality at a fraction of the size, with transparency to boot.
You still meet BMP in older Windows software, some scanners and simple programming exercises.
What opens a .bmp file?
The .bmp format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- Photos
- Paint
- any browser
macOS
- Preview
- any browser
Linux
- Image Viewer
- GIMP
Web
- Most browsers
Open a .bmp file step by step
- Confirm the file really is a .bmp. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with Photos or Paint.
- On Mac, use Preview or any browser.
- On Linux, try Image Viewer or GIMP.
- Still stuck? Convert the .bmp to PNG, which opens more widely.
Why can't I open my .bmp file?
Almost always because no installed app understands BMP. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .bmp at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
How to convert a .bmp file
You can convert a .bmp file to PNG, JPG, WebP using a conversion tool or the export menu of an app that opens it.
Convert images free: ImageConvert
What is the .bmp file signature (magic bytes)?
A .bmp file starts with the hex bytes 42 4D, which read as BM in ASCII. Programs identify BMP by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for BMP. For a full breakdown, see the BMP file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| 42 4D | 0 | BM | 'BM' |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .bmp file?
BMP is an old, simple Windows image format that stores pixels with little or no compression. Files are large and quality is perfect, which suits some technical uses, but for everyday sharing almost anything else is a better choice.
Why is my BMP file so big?
BMP stores pixels with little compression. Convert to PNG for the same lossless quality at a much smaller size.