AZW3 is the current Kindle format, which replaced MOBI. TXT is plain text, with no markup of any kind. calibre sits between the two, and this page says exactly what happens to an AZW3 file on the way to becoming a TXT one.
What runs when an AZW3 file becomes TXT
calibre the ebook-convert binary, on a machine we rent and watch. Your AZW3 file is uploaded once, calibre runs once, the TXT comes back, and neither file is kept. AZW3 to TXT 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 AZW3 into the TXT
The reading order and the chapter split of the AZW3 file. calibre rebuilds it as a book on the way to TXT, rather than as a pile of pages.
Cover art and book metadata, which calibre carries from the AZW3 container into the TXT one.
What AZW3 to TXT costs you
Fixed layout. calibre reflows the AZW3 text by design, because a TXT is meant to be read at any font size on any screen width.
Heading tags, tables, bold, text colour and font choices, and this is measured rather than assumed: we put an EPUB carrying a heading, a table, bold text, a colour and a font through every ebook target and read each result back with calibre. The TXT does not carry heading tags, tables, bold, text colour and font choices at all. What a device then DISPLAYS is a separate question, and one no measurement here reaches.
If a model is going to read the TXT
The words all survive, and the heading STRUCTURE does not: TXT has no tag for a heading, so calibre writes them as styled paragraphs. A model reading the TXT gets the text in order and has to infer the sections from it, which is exactly the work AZW3 was saving it. If a model is the reader, convert to Markdown instead.
AZW3 to TXT, measured rather than promised
Running AZW3 to TXT against the real engine with a real file, calibre wrote 219 bytes of TXT in 0.6 seconds, machine otherwise idle. That is one AZW3 file on one day and not an average, which is why the number is given together with the file that produced it.
The AZW3 to TXT verdict was reached by reading the text back, meaning the output decodes as readable text and still carries the witness word, which is the only check a plain text target allows. 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 TXT file has anything inside it.
The same AZW3 file, sent somewhere else
Other outputs the probe measured out of an AZW3 file, so the cost of choosing TXT can be read against something. Sizes do not compare across engines, because each family was probed with its own AZW3 witness file.
AZW3 to PDF: 62,065 bytes in 1.8 seconds, verified by a format signature.
AZW3 to DOCX: 23,936 bytes in 0.6 seconds, verified by a format signature.
AZW3 to EPUB: 22,666 bytes in 0.7 seconds, verified by a format signature.
AZW3 to RTF: 2,512 bytes in 0.6 seconds, verified by a format signature.
Other ways into TXT, and what they measured
Among the published routes into TXT, AZW3 is the ninth largest output of the 11 measured. The witness files differ, so this ranks the probe run and not your document.
CSV to TXT: 114 bytes in under a tenth of a second.
HTML to TXT: 270 bytes in under a tenth of a second.
JSON to TXT: 264 bytes in under a tenth of a second.
MD to TXT: 264 bytes in under a tenth of a second.
MOBI to TXT: 219 bytes in 0.5 seconds.
What we will not pretend about AZW3 to TXT
An AZW3 file over 50 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
An AZW3 to TXT 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.
Your headings stop being headings. TXT has no tag for one, so calibre writes them as styled paragraphs. The table of contents is built before that happens and survives; what you lose is the structure INSIDE the text, which matters the moment something reads the file rather than displays it.
The AZW3 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 TXT timing below is a measurement of one small file and not a guarantee about your thousand page one.
One AZW3 file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
AZW3 to TXT: what people ask
What actually converts my AZW3 file to TXT?
calibre does it, the ebook-convert binary, on a machine we rent and watch. Not a browser trick and not somebody else service: the AZW3 file is uploaded once, calibre runs once, the TXT comes back, and neither file is kept afterwards.
How long does AZW3 to TXT take?
On the file the probe used, calibre took 0.6 seconds and wrote 219 bytes of TXT. That is one real measurement on one real AZW3 file, not an average and not a promise about yours: a larger AZW3 takes longer, and past 120 seconds the run is stopped.
What do I lose going from AZW3 to TXT?
The one to know about first: Fixed layout. calibre reflows the AZW3 text by design, because a TXT is meant to be read at any font size on any screen width.
Does the table of contents survive from AZW3 to TXT?
It does, as long as your AZW3 file has real headings rather than text that merely looks like headings. calibre builds the TXT contents from the heading structure it finds, and hand-formatted big bold lines are not a structure.
Is AZW3 to TXT free?
There is a free allowance every month, and one AZW3 to TXT 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 TXT.