.BMP file signature
A BMP image data file begins with the bytes 42 4D (BM in ASCII) at the start of the file. The signature is the same whatever the file is named, which is why a renamed or extensionless BMP file is still recognisable.
Signature
| Offset | Hex | ASCII |
|---|---|---|
| 0 | 42 4D | BM |
MIME type: image/bmp · usual extensions: .bmp
How to check a file's signature
Without installing anything: drop the file on our detector. It reads the bytes in your browser and shows the hex dump alongside the verdict; nothing is uploaded.
macOS and Linux (Terminal):
xxd -l 32 file.bmp
file file.bmpWindows (PowerShell):
Format-Hex -Path file.bmp -Count 32If the bytes do not match
A file named .bmp whose first bytes are something else is not a BMP file. The common explanations are a wrong or deliberately misleading extension, a download that saved an HTML error page instead of the file, or a container such as ZIP wrapping the real content. The detector reports what the bytes say; the BMP guide explains what a genuine file should contain.