BMP is an uncompressed image format that stores pictures as a grid of colored dots

A BMP file (short for bitmap) is a way of storing an image on your computer. Instead of describing a picture with instructions — "draw a red circle here" — a BMP file stores it as a grid of tiny colored squares, one for each pixel on your screen. Each square gets its own color information, which is why BMP files tend to be large: they don't throw away any detail, but they also don't try to shrink the file down.

You'll most often see BMP files as simple graphics, icons, or screenshots on Windows computers. They're rarely the best choice for photos or complex images anymore, but they're still around because Windows has supported them since the 1980s and some older software expects them.

Key Takeaways

  • BMP files store images as a grid of colored pixels without compression, making them larger than formats like JPG or PNG.
  • Windows uses BMP for system graphics, wallpapers, and some icons, which is why you'll see them most on Windows machines.
  • BMP files are uncompressed, so opening and editing them is fast, but sharing them online or storing many of them wastes space.
  • You can open a BMP file with any image viewer, and convert it to JPG or PNG if you need a smaller file for email or the web.

How BMP files store color information

When you take a photo or create an image, your computer needs to remember the color of every single pixel. A BMP file does this straightforwardly: it writes down the color of pixel one, then pixel two, then pixel three, all the way across and down the image. There's no shortcut, no compression, no "this area is mostly blue so I'll just note that once."

This means a BMP file the size of your screen (say, 1920 by 1080 pixels) will be several megabytes, even if it's just a solid color. A JPG file of the same image might be 50 kilobytes. The trade-off is that BMP files are simple to read — your computer doesn't have to do any math to decode them — and they don't lose any detail in the process.

Where you'll actually see BMP files

Windows system files use BMP for wallpapers, cursors, and some built-in icons. If you've ever customized your desktop background on an older Windows machine, you may have picked a .bmp file. Some printers and industrial equipment also expect BMP files because the format is so old and stable that it's may provide to work.

Outside of Windows and specialized equipment, BMP is rare. Web browsers display them, but websites almost never use them because the file size is wasteful. Photo editing software opens them without trouble, but photographers use JPG or PNG instead. If you find a BMP file on your computer, it's usually either a system file you shouldn't touch, or something you can safely convert to another format.

Opening and converting BMP files

You don't need special software to open a BMP file. Windows Photo Viewer, Preview on Mac, or any image viewer will open it. If you want to edit it, you can use Paint (built into Windows), Photoshop, GIMP (free), or any other image editor.

To convert a BMP to a smaller format, right-click the file in Windows, choose "Open with," and pick Paint. Then go to File > Save As and choose JPG or PNG from the dropdown. PNG is usually the better choice if the image has text or sharp edges; JPG is better for photos. The converted file will be much smaller and work anywhere a BMP would.

BMP versus PNG and JPG

BMP, PNG, and JPG are three different ways to store the same picture. BMP is uncompressed and large. PNG compresses the file without losing any detail, so it's smaller than BMP but larger than JPG, and it's the standard for graphics, screenshots, and anything with text. JPG compresses by throwing away some color detail your eye probably won't notice, making it tiny — ideal for photos and web use.

If you're sending an image to someone, storing it in the cloud, or posting it online, convert it to PNG or JPG. If you're working with system files or old equipment that specifically asks for BMP, leave it alone. For everyday use, PNG is the safest middle ground: it's small, it preserves quality, and everything can open it.

When BMP files cause problems

The main problem with BMP is file size. A folder of BMP screenshots will fill up your storage much faster than the same screenshots saved as PNG. If you're trying to email a BMP file or upload it to a website, you may hit size limits that don't apply to PNG or JPG.

Some older software or hardware devices may request BMP specifically, but this is increasingly rare. If you encounter a system that won't accept PNG or JPG, converting to BMP is straightforward — but it's usually worth asking whether the system can accept a modern format instead, since BMP is an old standard that newer tools have moved past.

Frequently Asked Questions

Can I edit a BMP file?

Yes. Any image editor, including the free Paint program on Windows, can open and edit BMP files. After editing, you can save it as BMP again or convert it to PNG or JPG.

Is BMP the same as a bitmap?

Bitmap is the general term for any image stored as a grid of pixels. BMP is a specific file format. All BMP files are bitmaps, but not all bitmaps are BMP files — PNG and JPG are also bitmaps.

Why is my BMP file so large?

Because BMP doesn't compress the image. It stores the color of every pixel without any shortcuts. Converting it to PNG will shrink it significantly while keeping the same quality.

Do I need to convert my BMP files to something else?

Only if you plan to share them, store many of them, or use them on the web. If they're system files or you rarely touch them, there's no need to convert. If you do convert, PNG is the safest choice for most images.