GIF is a palette of at most 256 colours, all-or-nothing transparency, and animation. BMP is raw uncompressed pixels, which is why the files are so large. ImageMagick sits between the two, and this page says exactly what happens to a GIF file on the way to becoming a BMP one.
What runs when a GIF file becomes BMP
ImageMagick 6.9.12, on a machine we rent and watch. Your GIF file is uploaded once, ImageMagick runs once, the BMP comes back, and neither file is kept. GIF to BMP is one of the 3649 pairs that engine was probed on with a real file, which is why it has a page here and why the pairs the probe could not prove do not.
What survives from the GIF into the BMP
The pixel dimensions of your GIF file. The BMP comes out the size the GIF went in, because nothing on this path resizes anything.
What GIF to BMP costs you
Transparency. BMP has no alpha channel, so the engine composites your GIF image onto white before encoding. Without that step ImageMagick lays black underneath, and a transparent GIF logo comes back as a black rectangle.
Every frame of the GIF but the first. GIF can hold an animation and BMP cannot, so frame one is what comes back. The alternative would be one numbered BMP file per frame and no single answer to hand you.
If a model is going to read the BMP
A BMP file is pixels, and pixels are expensive for a model to read. Handed this BMP, an assistant spends its budget looking at the picture rather than reading it, and it will paraphrase what it thinks it saw. If your GIF is mostly words, the useful move is to pull the text out of it, not to change which picture format holds it.
GIF to BMP, measured rather than promised
Running GIF to BMP against the real engine with a real file, ImageMagick wrote 16,984 bytes of BMP in under a tenth of a second, machine otherwise idle. That is one GIF file on one day and not an average, which is why the number is given together with the file that produced it.
The GIF to BMP verdict was reached by a weak signature, meaning one or two bytes only, which is real evidence but leaves room for coincidence. Which check was used matters, because they do not all prove the same thing, and a status code of 200 proves nothing whatsoever about whether the BMP file has anything inside it.
The same GIF file, sent somewhere else
Other outputs the probe measured out of a GIF file, so the cost of choosing BMP can be read against something. Sizes do not compare across engines, because each family was probed with its own GIF witness file.
GIF to PDF: 1,092,578 bytes in 0.9 seconds, verified by a format signature.
GIF to JPG: 20,559 bytes in under a tenth of a second, verified by a format signature.
GIF to PNG: 3,894 bytes in under a tenth of a second, verified by a format signature.
GIF to TIFF: 848,536 bytes in 0.2 seconds, verified by a format signature.
GIF to MP4: 54,682 bytes in 0.3 seconds, verified by ffprobe.
GIF to WEBM: 49,644 bytes in 2.0 seconds, verified by ffprobe.
Other ways into BMP, and what they measured
Among the published routes into BMP, GIF is the tenth largest output of the 10 measured. The witness files differ, so this ranks the probe run and not your document.
HEIC to BMP: 72,138 bytes in under a tenth of a second.
HEIF to BMP: 72,138 bytes in under a tenth of a second.
ICO to BMP: 72,138 bytes in under a tenth of a second.
SVG to BMP: 72,138 bytes in under a tenth of a second.
TIFF to BMP: 72,138 bytes in under a tenth of a second.
What we will not pretend about GIF to BMP
A GIF file over 25 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A GIF to BMP run that passes 30 seconds is killed, and the ImageMagick process is killed with it. A run left behind would sit on one of the machine's two cores until somebody noticed.
No text is read out of the GIF anywhere on this path. Converting a picture to BMP never turns it into words, whatever the picture happens to contain.
ImageMagick was not saturated at sixteen simultaneous conversions: it held 47.5 a second while latency moved from 0.22 s to 0.34 s, and the service memory did not move off 51 MB. That is the measured headroom behind GIF to BMP, not a marketing number.
One GIF file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
GIF to BMP: what people ask
What actually converts my GIF file to BMP?
ImageMagick does it, 6.9.12, on a machine we rent and watch. Not a browser trick and not somebody else service: the GIF file is uploaded once, ImageMagick runs once, the BMP comes back, and neither file is kept afterwards.
How long does GIF to BMP take?
On the file the probe used, ImageMagick took under a tenth of a second and wrote 16,984 bytes of BMP. That is one real measurement on one real GIF file, not an average and not a promise about yours: a larger GIF takes longer, and past 30 seconds the run is stopped.
What do I lose going from GIF to BMP?
The one to know about first: Transparency. BMP has no alpha channel, so the engine composites your GIF image onto white before encoding. Without that step ImageMagick lays black underneath, and a transparent GIF logo comes back as a black rectangle.
Why did my transparent GIF background turn white in the BMP?
Because BMP has no alpha channel and something has to sit behind the picture. The engine puts white there on purpose. Left to itself ImageMagick puts black, and a transparent GIF logo comes back as a black rectangle. If you need the transparency, send the GIF to PNG or AVIF instead.
Is GIF to BMP free?
There is a free allowance every month, and one GIF to BMP conversion costs half a credit against it. When the allowance runs out the tool says so and stops, rather than quietly handing you a worse BMP.