BMP file format: what it is and how to use it

BMP is Windows' raw pixel format from 1990: an honest dump of the framebuffer with almost no compression and enormous file sizes. Learn when to use it and what to choose instead.

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What is a BMP file?

A .bmp file is an image in the Windows Bitmap format: a header describing dimensions and bit depth, then the pixel array nearly raw (optional weak RLE aside), rows usually stored bottom-up. It exists since Windows 3.0, is trivially simple to read or write, and is huge by design: every pixel occupies its full footprint.

When should you use BMP?

  • Embedded and legacy pipelines: firmware, old Windows tools and screen captures still emit .bmp.
  • Teaching and debugging: the format is transparent enough to inspect byte by byte.
  • Pixel-exact intermediates: when speed matters more than size on local scratch work.

When is another format a better fit?

For everything else, PNG stores the same pixels losslessly at a fraction of the size; TIFF is the professional uncompressed container; JPG or WebP serve delivery. BMP's only real edge is that you can write a reader in an afternoon.

The short version: BMP is the uncompressed Windows native: convert it to PNG and lose nothing but the weight.

How to open a BMP file

On Windows

Double-click the file, or open it with Paint.

On macOS

GIMP opens BMP files on macOS.

In your browser

Open BMP files right in a browser tab or with the dexrr viewer. No install, no upload.

Also opens in

  • Any web browser
  • Paint
  • GIMP
  • IrfanView

View or convert BMP files

A quick preview or a new format. No install, no upload.

View BMP files Preview and inspect BMP files Convert to BMP Turn files into BMP BMP to PNG Portable Network Graphics BMP to TIFF Tagged Image File Format BMP to TGA Truevision TGA / TARGA

BMP technical details

Full name
Windows Bitmap
Extensions
.bmp .dib
MIME type
image/bmp, image/x-ms-bmp
Magic bytes
42 4D (BM)
Compression
None (uncompressed)
Developer
Microsoft
Specification
learn.microsoft.com

BMP questions, answered

How do I open a .bmp file?

Every OS, viewer and editor opens it natively. It is one of the oldest formats still supported. dexrr displays and converts bmp files directly in your browser.

Can I convert BMP files online?

Yes, dexrr converts bmp locally in your browser: BMP to PNG for a lossless shrink or BMP to JPG for photos.

Is BMP better than PNG?

Never for storage. PNG is lossless too and far smaller. BMP's only advantage is the simplicity of its layout for manual tools and legacy systems.

Why is my BMP file so huge?

It stores every pixel uncompressed: a 12-megapixel photo needs ~36 MB as BMP. Convert to PNG for the same image at a fraction of the size.

Is the BMP format outdated?

As a distribution format, decades ago, but its trivial simplicity keeps it alive in Windows internals, embedded systems and screenshots.