Ebook formats are tied to devices more tightly than any other kind of file. Pick what you have and what you're reading on; we'll show the one conversion that works, what it changes, and when you don't need to convert at all.
The extension often lies: a .azw can be an old MOBI, a .epub can be locked by DRM, and a .pdf can be a stack of scanned photos. Drop in a book and your browser reads its structure without uploading it. For EPUB that means the OPF package, spine, fonts, accessibility metadata and encryption. For MOBI and AZW3 it means the Palm database header, the MOBI header and the EXTH metadata records. It also reads FB2, CBZ comics and PDF.
Reflowable books wrap to your screen and let you choose the text size. Fixed-layout ones keep the printed page. That one difference decides which conversions make sense.
A reflowable book is laid out by the reader at whatever text size you pick. A PDF page was laid out once, for paper, and the screen can only shrink it to fit. Pick a device and the work out below uses its real screen size and pixel density. Character widths are measured from the serif font your browser actually renders, and the previews keep each screen's true proportions.
The ferry left at six, as it had every morning for forty years, and Mara watched the harbour lights go out one by one behind it. She had come to the island to catalogue a library that nobody had opened since the war: eleven rooms of shelves, a ledger in three hands, and a smell of salt and old glue that followed her into sleep.
On the first day she counted spines. On the second she found the letters, folded into the books like pressed flowers, each one addressed to a lighthouse that the maps said had never been built.
By the end of the week she had stopped counting anything at all, and started reading.
The ferry left at six, as it had every morning for forty years, and Mara watched the harbour lights go out one by one behind it. She had come to the island to catalogue a library that nobody had opened since the war: eleven rooms of shelves, a ledger in three hands, and a smell of salt and old glue that followed her into sleep.
On the first day she counted spines. On the second she found the letters, folded into the books like pressed flowers, each one addressed to a lighthouse that the maps said had never been built.
By the end of the week she had stopped counting anything at all, and started reading. The ferry left at six, as it had every morning for forty years, and Mara watched the harbour lights go out one by one behind it.
She had come to the island to catalogue a library that nobody had opened since the war: eleven rooms of shelves, a ledger in three hands, and a smell of salt and old glue that followed her into sleep. On the first day she counted spines.
Page counts assume a 90,000-word novel, 0.3-inch screen margins, 1.45 line spacing and a measured average of 0.429 em per character in serif type, with a little allowance for line breaks. Real readers add headers, footers and hyphenation, so treat the counts as estimates within about 15%. Physical sizes come from each screen's pixel density. The previews are scaled down, not shown at actual size.
Each page explains exactly what's kept and what changes, with a typical result.
How to recognise each format, what it's built from, and which DRM schemes are used with it. Amazon's MOBI and AZW3 are Palm OS databases underneath, so their signature sits at byte 60, not byte 0.
The other toolboxes, with a typical job for each.