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BMP file format (.bmp)

Uncompressed Windows bitmap. Large but trivially readable.

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What is a BMP file?

In short: A BMP file (.bmp) is an image file in the BMP format. BMP stores pixels as a plain array with a small header, and in its usual form applies no compression at all. It can be converted to JPG, PNG or WEBP for free in a web browser with iHateFiles, without uploading it.

Introduced with Microsoft Windows in 1985 as the format the operating system itself drew from.

BMP stores pixels as a plain array with a small header, and in its usual form applies no compression at all. That makes it very simple to read and write, and very large: a 4000 by 3000 photograph is about 48 MB regardless of what is in it.

What BMP is good at

  • Absolutely lossless, with no compression artefacts of any kind
  • Trivial for software to read, which is why old tools favour it
  • Newer headers support an alpha channel

Where BMP falls short

  • Enormous compared to anything compressed
  • Metadata support is minimal
  • Rarely accepted by websites or messaging apps

When to use BMP

Use BMP when a piece of software specifically demands it. For everything else, PNG is lossless too and a fraction of the size.

How to open a BMP file

Windows natively, and every image editor. Browsers display it, though few sites accept it.

Opening a .bmp file on each platform
WindowsOpens everywhere on Windows — it is Windows’ own bitmap format.
macOSPreview opens it.
LinuxEvery viewer reads BMP.
PhoneUsually needs a file manager with a viewer built in.
In a browserChrome, Firefox and Safari all display BMP, though nobody serves it on the web.

The thing that usually goes wrong

The file size surprises people. There is no compression to speak of, so the size depends only on the dimensions, not on how complicated the image is.

Questions

What is a BMP file?

Uncompressed Windows bitmap. Large but trivially readable. Files use the .bmp extension.

How do I open a BMP file?

Most image software opens BMP directly. If yours does not, convert it here to something more common. It takes a few seconds and nothing is uploaded.

Can I convert BMP for free?

Yes. Every conversion here is free and unlimited, because your own device does the work rather than a server we have to pay for.

Is BMP lossless?

Yes. BMP stores every pixel exactly, at the cost of a larger file.