WOFF is a web font, which is a compressed wrapper around a TTF or an OTF. TTF is a TrueType font, the kind almost every system ships with. fontTools sits between the two, and this page says exactly what happens to a WOFF file on the way to becoming a TTF one.
What runs when a WOFF file becomes TTF
fontTools in our own Python, on a machine we rent and watch. Your WOFF file is uploaded once, fontTools runs once, the TTF comes back, and neither file is kept. WOFF to TTF 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 WOFF into the TTF
Every glyph, unchanged. This pair does not redraw anything: the outlines that leave the WOFF arrive in the TTF point for point, so the letters render exactly as the designer drew them. The engine counts them on the way out and refuses the file if the count moved. Measured on this pair: the probe file came back at 759 572 bytes in 0.1 s.
Hinting, kerning pairs and OpenType features: the tables that tell a renderer how to space and substitute glyphs. This pair moves the container around them rather than through them.
A font you can install. A WOFF is made to be fetched by a browser, not double-clicked; the TTF is the form your operating system, your word processor and your design tool expect.
What WOFF to TTF costs you
Nothing about the WOFF itself, and that is worth saying plainly rather than inventing a caveat. What this pair changes is how the font is packaged, never what it draws.
The size advantage. A WOFF was compressed for the network; the TTF is not, so expect the file to grow by two to three times. Measured on DejaVu Sans: 258 392 bytes of WOFF2 unpack to 759 572 bytes.
Any licence to use it. A font served on a web page is often licensed for that page and nothing else. Converting it does not change what you are allowed to do with it, and this page is not going to pretend otherwise.
Where WOFF and TTF files come from
WOFF. A W3C recommendation from 2012, made for one job: shipping a font over HTTP. It wraps an existing TrueType or PostScript font and compresses it with zlib. Measured on DejaVu Sans: 759 720 bytes become 379 328.
TTF. Everything that makes fonts writes it, and every operating system installs it. Its outlines are quadratic curves, which is what distinguishes it from OTF and what decides which conversions are possible at all.
If a model is going to read the TTF
Structure is what survives from the WOFF file, and structure is what a model needs. WOFF in, TTF out, with the heading tree intact instead of flattened into one long paragraph.
WOFF to TTF, measured rather than promised
Running WOFF to TTF against the real engine with a real file, fontTools wrote 759,572 bytes of TTF in 0.1 seconds, machine otherwise idle. That is one WOFF file on one day and not an average, which is why the number is given together with the file that produced it.
The WOFF to TTF verdict was reached by reading the font back with fontTools and checking what kind of outlines it holds, meaning the output was read back and recognised. 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 TTF file has anything inside it.
Other ways into TTF, and what they measured
Among the published routes into TTF, WOFF is the first largest output of the 2 measured. The witness files differ, so this ranks the probe run and not your document.
WOFF2 to TTF: 752,580 bytes in 0.8 seconds.
What we will not pretend about WOFF to TTF
A WOFF file over 25 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A WOFF to TTF run that passes 50 seconds is killed, and the fontTools process is killed with it. A run left behind would sit on one of the machine's two cores until somebody noticed.
A WOFF wraps either kind of outline, so this pair works for some files and not others. Most web fonts wrap TrueType, which is why WOFF to TTF usually works and WOFF to OTF usually does not. The refusal is immediate, costs nothing, and names the target that would have worked for your file.
One WOFF file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
WOFF to TTF: what people ask
What actually converts my WOFF file to TTF?
fontTools does it, in our own Python, on a machine we rent and watch. Not a browser trick and not somebody else service: the WOFF file is uploaded once, fontTools runs once, the TTF comes back, and neither file is kept afterwards.
How long does WOFF to TTF take?
On the file the probe used, fontTools took 0.1 seconds and wrote 759,572 bytes of TTF. That is one real measurement on one real WOFF file, not an average and not a promise about yours: a larger WOFF takes longer, and past 50 seconds the run is stopped.
What do I lose going from WOFF to TTF?
The one to know about first: Nothing about the WOFF itself, and that is worth saying plainly rather than inventing a caveat. What this pair changes is how the font is packaged, never what it draws.
Will the TTF look different from the WOFF?
No. Not slightly, not in edge cases: the outlines are copied rather than redrawn, so every glyph has the same coordinates it had before. The engine counts the glyphs on the way out and refuses the file if the count moved, which is the one way this could go wrong silently.
Am I allowed to do this?
That depends on the font, and this tool cannot tell you. A font served on a web page is often licensed for that page and nothing else; converting it does not change what the licence permits. The conversion is technical, the permission is not.
Why did the file get bigger?
Because a WOFF is compressed for the network and a TTF is not. Measured: 258 392 bytes of WOFF2 unpack to 759 572 bytes. Nothing was added; the compression was removed.
Is WOFF to TTF free?
There is a free allowance every month, and one WOFF to TTF 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 TTF.