HEIC is what an iPhone writes unless you tell it not to: HEVC compression inside an ISO container, about half the size of the JPEG it replaced. JPEG is lossy compression tuned for human vision, and no alpha channel at all. ImageMagick sits between the two, and this page says exactly what happens to a HEIC file on the way to becoming a JPG one.
What runs when a HEIC file becomes JPG
ImageMagick 6.9.12, on a machine we rent and watch. Your HEIC file is uploaded once, ImageMagick runs once, the JPG comes back, and neither file is kept. HEIC to JPG 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 HEIC into the JPG
The pixel dimensions of your HEIC file. The JPG comes out the size the HEIC went in, because nothing on this path resizes anything.
What HEIC to JPG costs you
Transparency. JPG has no alpha channel, so the engine composites your HEIC image onto white before encoding. Without that step ImageMagick lays black underneath, and a transparent HEIC logo comes back as a black rectangle.
Every page of the HEIC but the first. A HEIC file can hold several images in one container; a JPG file holds exactly one.
If a model is going to read the JPG
A JPG file is pixels, and pixels are expensive for a model to read. Handed this JPG, an assistant spends its budget looking at the picture rather than reading it, and it will paraphrase what it thinks it saw. If your HEIC is mostly words, the useful move is to pull the text out of it, not to change which picture format holds it.
HEIC to JPG, measured rather than promised
Running HEIC to JPG against the real engine with a real file, ImageMagick wrote 1,666 bytes of JPG in under a tenth of a second, machine otherwise idle. That is one HEIC file on one day and not an average, which is why the number is given together with the file that produced it.
The HEIC to JPG verdict was reached by a format signature, meaning at least four bytes unique to the format were found at the right offset. 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 JPG file has anything inside it.
The same HEIC file, sent somewhere else
Other outputs the probe measured out of a HEIC file, so the cost of choosing JPG can be read against something. Sizes do not compare across engines, because each family was probed with its own HEIC witness file.
HEIC to PDF: 94,782 bytes in under a tenth of a second, verified by a format signature.
HEIC to PNG: 1,403 bytes in under a tenth of a second, verified by a format signature.
HEIC to WEBP: 416 bytes in under a tenth of a second, verified by a format signature.
HEIC to GIF: 2,918 bytes in 0.1 seconds, verified by a format signature.
HEIC to TIFF: 90,264 bytes in under a tenth of a second, verified by a format signature.
Other ways into JPG, and what they measured
Among the published routes into JPG, HEIC is the sixth largest output of the 13 measured. The witness files differ, so this ranks the probe run and not your document.
PNG to JPG: 1,568 bytes in under a tenth of a second.
WEBP to JPG: 2,340 bytes in under a tenth of a second.
PDF to JPG: 5,782 bytes in 0.1 seconds.
GIF to JPG: 20,559 bytes in under a tenth of a second.
BMP to JPG: 1,568 bytes in under a tenth of a second.
What we will not pretend about HEIC to JPG
A HEIC file over 25 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A HEIC to JPG 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.
Until the end of August this machine could not read a HEIC at all, and reported the opposite. ImageMagick declared HEIC readable, but libheif carried only its AV1 plugins, which serve AVIF; the HEVC decoder was absent, and a HEIC decoded quietly as something else. The plugin was installed on the 30th, and that is the whole reason this pair exists.
The HEIC to JPG proof used a file genuinely encoded in HEVC, and that detail is not pedantry: ImageMagick refuses to write HEIC and hands you a PNG under that name if you ask it to, so a HEIC forged for the test would have made a false result look like a true one. The JPG it produced was 1,666 bytes, recognised by a format signature.
No text is read out of the HEIC anywhere on this path. Converting a picture to JPG 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 HEIC to JPG, not a marketing number.
One HEIC file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
HEIC to JPG: what people ask
What actually converts my HEIC file to JPG?
ImageMagick does it, 6.9.12, on a machine we rent and watch. Not a browser trick and not somebody else service: the HEIC file is uploaded once, ImageMagick runs once, the JPG comes back, and neither file is kept afterwards.
How long does HEIC to JPG take?
On the file the probe used, ImageMagick took under a tenth of a second and wrote 1,666 bytes of JPG. That is one real measurement on one real HEIC file, not an average and not a promise about yours: a larger HEIC takes longer, and past 30 seconds the run is stopped.
What do I lose going from HEIC to JPG?
The one to know about first: Transparency. JPG has no alpha channel, so the engine composites your HEIC image onto white before encoding. Without that step ImageMagick lays black underneath, and a transparent HEIC logo comes back as a black rectangle.
Why did my transparent HEIC background turn white in the JPG?
Because JPG 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 HEIC logo comes back as a black rectangle. If you need the transparency, send the HEIC to PNG or WebP instead.
Is HEIC to JPG free?
There is a free allowance every month, and one HEIC to JPG 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 JPG.