wire / magic / bmp

BMP signature (BM)

A Windows bitmap (BMP) file begins with the 2-byte ASCII signature 'BM' (0x42 0x4D), followed by a 4-byte little-endian total file size. 'BM' is by far the most common of several possible bitmap-type marks.

magic kind signature status de-facto verification verified tier B file-signature@1

aka: BMP magic · bitmap · BM

file signature

magic: 42 4D @ offset 0

ascii: BM

.bmp.dib image/bmp

spec: Microsoft BITMAPFILEHEADER

bfType is the 16-bit value 0x4D42 stored little-endian => bytes 42 4D = 'BM'.
Bytes 2-5: bfSize, total file size in bytes, little-endian.
Bytes 10-13: bfOffBits, offset to the pixel array.
Rare alternative type marks ('BA','CI','CP','IC','PT') come from OS/2 and are essentially never seen.

provenance

source: https://learn.microsoft.com/en-us/windows/win32/api/wingdi/ns-wingdi-bitmapfileheader
version: Microsoft BITMAPFILEHEADER (bfType 0x4D42 = 'BM')
retrieved: 2026-05-29 · updated: 2026-05-29T00:00:00Z

BMP signature (BM)

file signature

provenance

see also