MOBI is the old Kindle format, and a very poor carrier of formatting. RTF is rich text that almost every word processor ever written can open. calibre sits between the two, and this page says exactly what happens to a MOBI file on the way to becoming an RTF one.
What runs when a MOBI file becomes RTF
calibre the ebook-convert binary, on a machine we rent and watch. Your MOBI file is uploaded once, calibre runs once, the RTF comes back, and neither file is kept. MOBI to RTF 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 MOBI into the RTF
The reading order and the chapter split of the MOBI file. calibre rebuilds it as a book on the way to RTF, rather than as a pile of pages.
Headings, and with them the table of contents: MOBI and RTF both carry a heading hierarchy calibre can map one onto the other.
Cover art and book metadata, which calibre carries from the MOBI container into the RTF one.
What MOBI to RTF costs you
Fixed layout. calibre reflows the MOBI text by design, because an RTF is meant to be read at any font size on any screen width.
Where MOBI and RTF files come from
RTF. Almost everything can write it, and that is the point: an RTF is plain text you can open in a text editor and read. It was the interchange format before there was an open standard, and it survives in exports from software too old or too small to ship anything better.
If a model is going to read the RTF
Structure is what survives from the MOBI file, and structure is what a model needs. MOBI in, RTF out, with the heading tree intact instead of flattened into one long paragraph.
MOBI to RTF, measured rather than promised
Running MOBI to RTF against the real engine with a real file, calibre wrote 2,489 bytes of RTF in 0.6 seconds, machine otherwise idle. That is one MOBI file on one day and not an average, which is why the number is given together with the file that produced it.
The MOBI to RTF 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 RTF file has anything inside it.
The same MOBI file, sent somewhere else
Other outputs the probe measured out of a MOBI file, so the cost of choosing RTF can be read against something. Sizes do not compare across engines, because each family was probed with its own MOBI witness file.
MOBI to PDF: 62,207 bytes in 1.9 seconds, verified by a format signature.
MOBI to DOCX: 24,070 bytes in 0.6 seconds, verified by a format signature.
MOBI to EPUB: 22,644 bytes in 0.6 seconds, verified by a format signature.
MOBI to TXT: 219 bytes in 0.5 seconds, verified by reading the text back.
MOBI to AZW3: 61,343 bytes in 0.6 seconds, verified by a format signature.
Other ways into RTF, and what they measured
Among the published routes into RTF, MOBI is the sixth largest output of the 11 measured. The witness files differ, so this ranks the probe run and not your document.
ODT to RTF: 4,214 bytes in 1.1 seconds.
TXT to RTF: 484 bytes in under a tenth of a second.
PDF to RTF: 99,461 bytes in 0.8 seconds.
DOC to RTF: 4,321 bytes in 1.1 seconds.
DOCX to RTF: 4,205 bytes in 1.1 seconds.
What we will not pretend about MOBI to RTF
A MOBI file over 50 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A MOBI to RTF run that passes 120 seconds is killed, and the calibre process is killed with it. A run left behind would sit on one of the machine's two cores until somebody noticed.
The MOBI file used to prove this pair was short. calibre is allowed 120 seconds and a long book can genuinely need all of them, so the RTF timing below is a measurement of one small file and not a guarantee about your thousand page one.
One MOBI file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
MOBI to RTF: what people ask
What actually converts my MOBI file to RTF?
calibre does it, the ebook-convert binary, on a machine we rent and watch. Not a browser trick and not somebody else service: the MOBI file is uploaded once, calibre runs once, the RTF comes back, and neither file is kept afterwards.
How long does MOBI to RTF take?
On the file the probe used, calibre took 0.6 seconds and wrote 2,489 bytes of RTF. That is one real measurement on one real MOBI file, not an average and not a promise about yours: a larger MOBI takes longer, and past 120 seconds the run is stopped.
What do I lose going from MOBI to RTF?
The one to know about first: Fixed layout. calibre reflows the MOBI text by design, because an RTF is meant to be read at any font size on any screen width.
Does the table of contents survive from MOBI to RTF?
It does, as long as your MOBI file has real headings rather than text that merely looks like headings. calibre builds the RTF contents from the heading structure it finds, and hand-formatted big bold lines are not a structure.
Is MOBI to RTF free?
There is a free allowance every month, and one MOBI to RTF 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 RTF.