What a BMP file is
What a .BMP file is, what it does well, what opens one, and how to convert it — with every conversion running in your own browser.
What a BMP file is
A BMP is about as simple as an image file gets: a short header, then the pixels, one after another, usually with no compression at all. Its size is close to width times height times bytes per pixel, which for a phone photograph runs to tens of megabytes.
That simplicity is the only reason it survives. A BMP can be read by code that does almost nothing, which is why it turns up in embedded systems, in older Windows tooling, and as the format some scanner or industrial device insists on writing.
For anything else it is the wrong choice. It has no transparency in any form most software will honour, no animation, no metadata worth the name, and a file size that no modern format comes close to.
Where it came from
BMP is a Microsoft format from the mid-1980s, defined for Windows and OS/2 and essentially unchanged since. It has never been a web format and was never meant to be one — it exists because a system needed a bitmap on disk that its own graphics layer could load without thinking.
BMP at a glance
| Property | BMP |
|---|---|
| Compression | None, stored as written |
| Colour | 8 bits per channel |
| Transparency | None |
| Animation | No |
| Keeps EXIF | No |
| Browser support | Every browser since 1995 |
| Size of a photograph | 8 to 20 times a JPG |
| Published | 1990 |
BMP at a glance
- Nothing is compressed. The file size follows almost directly from the dimensions, which is why these files are so much larger than everything else here.
- Colour is stored as 8 bits per channel, which is enough for the gradients in a photograph to look smooth rather than stepped.
- There is no transparency. Converting an image that had some produces a solid background, and which colour it becomes is a choice the converter has to make for you.
- There is no standard place for camera data, dates, or copyright, so anything the source carried is dropped on the way in.
What it is good at
- Nothing is discarded. What you put in is what comes back, however many times you save it.
- Every browser in use reads it, and has for long enough that it needs no fallback.
Where it falls short
- No transparency of any kind. A transparent area becomes a solid colour, usually white or black.
- One frame only. An animation converted to it keeps the first frame and drops the rest.
- No standard place for camera data, dates, or copyright, so those are lost on the way in.
- Roughly 8 to 20 times the size of a JPG of the same photograph at comparable quality.
What to use instead of BMP
- For anything that needs a transparent background — a logo, an icon, a cut-out — use PNG, or WebP if the file is destined for a web page you control.
- For anything that moves, use animated WebP. GIF also animates and is more widely accepted, but stores the same clip at several times the size with a fraction of the colours.
- For a smaller file at quality most people cannot tell apart, use WebP, or AVIF where the audience is on the web and encoding time is not a concern.
When to use BMP
Choose BMP when a specific program or device demands it. Some scanners, some embedded systems, and some older Windows tooling will accept nothing else, and in those cases the format's simplicity is exactly why.
Avoid BMP everywhere else. PNG stores the same pixels with no loss at a fraction of the size, opens in more software, and carries transparency. There is no situation where a BMP is better than a PNG other than a program that cannot read PNG.
What opens a BMP file
On a computer, BMP files open in Paint on Windows, Preview on macOS, GIMP.
Every browser in use displays them, so opening one is usually a matter of dragging it into a browser window.
Turn a BMP file into something else:
Produce a BMP file from something else:
Common problems with BMP
- The transparent background turned white.
- The format has no transparency at all, so the converter had to fill those pixels with something. Convert to PNG, WebP, or AVIF instead if the transparency matters, or set the background colour deliberately so it matches wherever the image will sit.
- The camera data and copyright fields have disappeared.
- The format has no standard place to keep them, so anything the source carried was dropped on the way in. Convert to a format that holds metadata if attribution matters, or keep the original alongside the converted copy as the record of where it came from.
- The file is far bigger than I expected.
- This format is not built for photographs, and a photograph is what makes it grow: there is no repetition for the compression to collapse. If it is a photograph, JPG, WebP, or AVIF will produce something dramatically smaller at quality most people cannot tell apart.
Converting a BMP file here
- Choose your file, or drag it onto the box. It is read from your device and goes no further.
- Set whatever the conversion offers — quality, size, background — and start it. Everything runs on your own machine, so a large image uses your memory and your processor rather than a queue somewhere.
- Download the result. Nothing is kept: leaving the page or resetting it releases the file and the converted copy alike.
Common questions
- Why is my BMP so enormous?
- Because it is not compressed. A BMP generally stores every pixel at full size with nothing collapsed, so a photograph that is three megabytes as a JPG can be thirty as a BMP. Converting it to almost anything else will shrink it dramatically, and converting to PNG will do so without losing a thing.
- Is there any reason to keep a BMP?
- Only if a specific program demands one. There is no quality advantage — PNG is also lossless and far smaller — and no capability advantage. If something in your workflow writes BMPs, converting them on the way out is the normal thing to do.
- Can a BMP hold transparency?
- Some variants of the format define an alpha channel, but support for it is inconsistent enough that it cannot be relied on — plenty of software reads the file and ignores the transparency entirely. If transparency matters, use PNG.
- How much smaller or larger will the file get?
- The table above states the size of the same photograph in each format against JPG, which is the closest thing to an answer that holds in general. The real figure depends on the picture: flat colour and sharp edges behave very differently from a photograph, and the ranges assume a photograph.
- How do I open a .BMP file?
- The software listed above reads them directly. If nothing on your machine will, converting to PNG or JPG is the reliable route — both open in everything, and the conversion happens here in your browser rather than on a server.
- Does converting a BMP file lose quality?
- It depends on what you convert it to rather than on what you convert from. Converting to a lossless format such as PNG preserves every pixel; converting to JPG, WebP, or AVIF discards detail permanently. Nothing recovers quality the file had already lost.
- Is converting from BMP free, and does it upload my file?
- Free, with no account, and nothing is uploaded. Every converter on this site reads your file with the browser's own file APIs, converts it using code running on your device, and hands the result back as a download. You can confirm that yourself in the Network panel of your browser's developer tools.
- Where does the conversion happen?
- In your browser, on your own device. There is no conversion server here to upload anything to, and no third-party service is involved. That is a statement about what the site does rather than a promise about how it handles uploads, because no upload takes place.