WOFF2 is the second web font format, compressed with Brotli. WOFF is a web font, which is a compressed wrapper around a TTF or an OTF. fontTools sits between the two, and this page says exactly what happens to a WOFF2 file on the way to becoming a WOFF one.
What runs when a WOFF2 file becomes WOFF
fontTools in our own Python, on a machine we rent and watch. Your WOFF2 file is uploaded once, fontTools runs once, the WOFF comes back, and neither file is kept. WOFF2 to WOFF 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 WOFF2 into the WOFF
Every glyph, unchanged. This pair does not redraw anything: the outlines that leave the WOFF2 arrive in the WOFF 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 377 532 bytes in 0.8 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.
Size, and this is the reason to do it. Measured on DejaVu Sans, 6253 glyphs: 759 720 bytes of WOFF2 become 379 328 bytes of WOFF, half the original. Nothing was removed to get there; it is compression, and the browser undoes it before rendering.
What WOFF2 to WOFF costs you
Nothing about the WOFF2 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 ability to double-click it. A WOFF is not installable: operating systems do not accept it, and design tools do not list it. It is made to be served over HTTP and read by a browser, which is the whole point.
Nothing else, and specifically not quality. This is compression, not resampling: the WOFF decompresses to the same bytes the WOFF2 held.
Where WOFF2 and WOFF files come from
WOFF2. A W3C recommendation from 2018 and what every browser prefers today. Same idea as WOFF, better compression: Brotli instead of zlib, plus a transform that rewrites the glyph table before compressing. Measured on DejaVu Sans: 759 720 bytes become 258 392, a third of the original.
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.
If a model is going to read the WOFF
Structure is what survives from the WOFF2 file, and structure is what a model needs. WOFF2 in, WOFF out, with the heading tree intact instead of flattened into one long paragraph.
WOFF2 to WOFF, measured rather than promised
Running WOFF2 to WOFF against the real engine with a real file, fontTools wrote 377,532 bytes of WOFF in 0.8 seconds, machine otherwise idle. That is one WOFF2 file on one day and not an average, which is why the number is given together with the file that produced it.
The WOFF2 to WOFF 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 WOFF file has anything inside it.
Other ways into WOFF, and what they measured
Among the published routes into WOFF, WOFF2 is the second largest output of the 3 measured. The witness files differ, so this ranks the probe run and not your document.
OTF to WOFF: 60,904 bytes in 0.2 seconds.
TTF to WOFF: 379,328 bytes in 0.1 seconds.
What we will not pretend about WOFF2 to WOFF
A WOFF2 file over 25 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A WOFF2 to WOFF 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 WOFF2 wraps either kind of outline, so this pair works for some files and not others. Most web fonts wrap TrueType, which is why WOFF2 to TTF usually works and WOFF2 to OTF usually does not. The refusal is immediate, costs nothing, and names the target that would have worked for your file.
One WOFF2 file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
WOFF2 to WOFF: what people ask
What actually converts my WOFF2 file to WOFF?
fontTools does it, in our own Python, on a machine we rent and watch. Not a browser trick and not somebody else service: the WOFF2 file is uploaded once, fontTools runs once, the WOFF comes back, and neither file is kept afterwards.
How long does WOFF2 to WOFF take?
On the file the probe used, fontTools took 0.8 seconds and wrote 377,532 bytes of WOFF. That is one real measurement on one real WOFF2 file, not an average and not a promise about yours: a larger WOFF2 takes longer, and past 50 seconds the run is stopped.
What do I lose going from WOFF2 to WOFF?
The one to know about first: Nothing about the WOFF2 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 WOFF look different from the WOFF2?
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.
How much smaller is the WOFF?
Measured on DejaVu Sans, a 6253 glyph font: 759 720 bytes of WOFF2 become 379 328 bytes of WOFF. Your font will differ, but the ratio holds: WOFF uses zlib and lands near a half.
Can I install the WOFF on my computer?
No, and that is not a limitation of this tool. A WOFF is a web format: browsers fetch it, operating systems do not install it. If you want to use the font locally, convert it to TTF or OTF instead.
Is WOFF2 to WOFF free?
There is a free allowance every month, and one WOFF2 to WOFF 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 WOFF.