What you are trading when you convert HEIC to BMP
Start with the number, because no other page seems willing to print it.
We converted a 12 megapixel HEIC through this exact tool and measured the result. The 1.38 MB original became a 34.33 MB bitmap — roughly 25 times larger.
That is not a flaw in the conversion. BMP stores three bytes for every pixel and compresses nothing, so the size is pure arithmetic: 4000 × 3000 × 3 bytes, plus a 54-byte header. Our output was 36,000,054 bytes, which is exactly that sum.
There is exactly one good reason to convert HEIC to BMP: something you cannot change is demanding a bitmap. If nothing is, you want JPG or PNG instead, and you will thank yourself for the disk space.
Who still needs a bitmap
BMP survives in the corners of computing where nothing ever gets rewritten.
Legacy Windows software. Applications written in the 1990s and early 2000s often read BMP and nothing else. Windows has understood the format natively since the beginning, so it became the safe choice and then never left.
Embedded displays. Arduino, STM32 and similar boards can push a bitmap to a screen with no decoding library at all. Every other format needs code you may not have room for.
Industrial and instrument software. Factory panels, inspection rigs and older laboratory equipment often specify uncompressed input, because deterministic read times matter more to them than storage does.
Resource compilers and toolchains. Some build pipelines still expect BMP for icons and embedded assets.
In all of these cases the requirement comes from outside you. Nobody picks BMP for themselves.
How to convert HEIC to BMP in 3 steps
1. Add your photos
Drag them onto the drop zone, paste from the clipboard, or click to browse. Add as many as you like — there is no cap and no account.
Nothing is uploaded at this step, or at any other one.
2. Press Convert
Each HEIC is decoded and written out as a 24-bit uncompressed bitmap. On an ordinary desktop that took us 779 milliseconds for a 12 megapixel photo, start to finish.
There is no quality setting, because BMP has nothing to tune. Uncompressed means uncompressed.
3. Download
Save each bitmap individually, or take the whole batch as one .zip.
Give the download a moment. These files are large by design, and your browser is writing tens of megabytes to disk per photo.
Why this page had to write its own BMP encoder
Here is something we found while building the site, and it is worth knowing if you ever build an image tool yourself.
Ask a browser canvas for
image/bmpand it hands you back a PNG. No error, no warning. Only the blob’s MIME type reveals it.
We verified that on Chrome 145, along with the same silent substitution for image/avif, image/gif and image/tiff. A browser-based converter that asks canvas for a BMP and ships whatever comes back is delivering a renamed PNG.
That would be visible the moment your legacy software opened it, which is exactly the software with no tolerance for surprises.
So the bitmap you download here is written byte by byte in our own code, the same way our HEIC to TIFF converter writes TIFF. We checked the output the obvious way: convert the same photo to PNG and to BMP, decode both, and compare pixels. Every channel of every pixel matched.
What is inside the file you get
Worth being specific, since compatibility is the entire point of asking for a bitmap.
The file is a 14-byte BITMAPFILEHEADER, then a 40-byte BITMAPINFOHEADER, then raw pixels. It is 24-bit, uncompressed BI_RGB, with rows stored bottom-up and channels in BGR order — all of which is what the original format specified.
That is the oldest and most widely understood variant in existence, and it is deliberate. Modern 32-bit BMP files with an alpha channel need a V4 or V5 header, and plenty of the ancient software people convert bitmaps for will refuse to open one.
Since a 24-bit bitmap has nowhere to keep transparency, any transparent pixels are composited onto white before writing, exactly the way JPEG handles the same problem.
What about the other BMP variants?
The format has accumulated a fair number of forms over thirty years, and it is worth saying which ones we deliberately skip.
8-bit palette BMP stores an index per pixel plus a colour table, which makes files roughly a third the size. It also caps the image at 256 colours, and turning a photograph into 256 colours requires quantisation that visibly damages it. Wrong trade for a photo.
RLE-compressed BMP exists, applies only to the palette forms, and is poorly supported by exactly the old software that would benefit. It compresses flat graphics well and photographs barely at all.
32-bit BMP with alpha needs a V4 or V5 header. Modern software reads it, but the legacy tools that motivate this page frequently do not, and a file that fails to open is worse than a file that is large.
So a photograph coming out of a HEIC gets the 24-bit form. It is the variant with the widest support and no surprises, which is the only thing anyone is really buying when they ask for a bitmap.
Opening the file afterwards
Nothing special is required, which is the whole appeal.
On Windows, Photos and Paint both open a bitmap directly, and have since long before either was rewritten. On a Mac, Preview opens it without complaint. Every image editor ever shipped will read it.
If your target is a piece of embedded or industrial software, it will normally document the exact variant it wants. Ours is the plain one that such documentation almost always describes.
BMP or PNG: how to decide
These two get compared constantly because both are lossless. They are not interchangeable.
| BMP | PNG | |
|---|---|---|
| Compression | None at all | Lossless, typically 2–3× smaller |
| Our 12 MP test file | 34.33 MB | 13.71 MB |
| Transparency | Not in the 24-bit form | Full alpha channel |
| Modern software | Universally readable | Universally readable |
| Very old software | Often the only option | Sometimes unsupported |
| Sensible default | No | Yes |
The rule is simple. If something specifically asked for a .bmp, give it a .bmp. In every other situation PNG gives you the same lossless pixels in a third of the space, which is why it is our homepage tool.
Why uploading a bitmap is the worst case
Every other HEIC to BMP converter we could find runs on a server. That means your photo goes up, and a 34 megabyte bitmap comes back down.
On a decent connection that download alone is several seconds per photo. On a phone it is a meaningful chunk of a data plan. Convert thirty photos and you have moved a gigabyte across the network to accomplish something your own processor could have done locally in under a second each.
Our measurement was 779 milliseconds to decode a 12 megapixel HEIC and write the complete bitmap, on an ordinary desktop.
There is also the privacy side, which applies to every tool here but bites harder when the payload is this big. Nothing you drop onto this page is transmitted anywhere. Load it, disconnect from the internet, and it keeps converting.
Converting a whole folder
Batch conversion works exactly as it does elsewhere on the site: add as many files as you like, convert them together, and download a single .zip.
The thing to watch is disk space rather than time. Thirty photos at 34 MB each is a gigabyte of bitmaps, and the zip barely helps — BMP data does compress in a zip, but you still need room for both.
If your target software will accept it, converting at a smaller pixel size is the single most effective thing you can do, since bitmap size scales directly with pixel count. Our HEIC resizer handles that, and halving the dimensions quarters the bitmap.
The bottom line
A BMP is the most compatible and least efficient way to store a photograph, and both halves of that sentence are the point.
Convert HEIC to BMP when something old and inflexible is asking for one, and not otherwise. Expect a file around 25 times the size of the original, get a 24-bit uncompressed bitmap that virtually anything can open, and keep the HEIC as the copy you actually store.
For everything else, PNG does the same job losslessly in a fraction of the space.