OTF to TTF Converter

OTF and TTF are both OpenType

An .otf file and a .ttf file are, in almost every case, the same kind of file. Both use the sfnt container the OpenType specification describes: a header, a table directory, and a set of tables identified by four-character tags such as cmap, head, name and GSUB. What differs is the table holding the glyph outlines. A font with TrueType outlines keeps them in glyf and loca and opens with the version tag 0x00010000. A font with PostScript outlines keeps them in a CFF or CFF2 table and opens with the tag OTTO. Convention names the first .ttf and the second .otf, which is why converting OpenType to TrueType is a real operation and not a rename.

The rasteriser decides what a file is by reading that version tag, not by reading the extension. A CFF font renamed to .ttf still works on Windows, macOS and Linux, and it is still a CFF font. If a tool rejected your file for being the wrong type, renaming it will not fix anything.

What actually changes in the conversion

TrueType outlines are quadratic Bézier curves with one off-curve control point per segment. PostScript outlines are cubic, with two. A cubic curve can be approximated by a chain of quadratic segments to any tolerance you pick, but it cannot generally be reproduced exactly, so a real OTF to TTF conversion redraws every curve in the font. At text sizes the difference is invisible. At poster sizes, or when the outlines feed a cutting plotter, an engraver or a 3D extrusion, the approximation error is something you can measure.

What survives and what does not

• Glyph shapes survive as an approximation. Good converters fit quadratics within a tolerance you cannot see; crude ones produce visible kinks at high contrast joins and on tight curves.
• Character mapping survives. The cmap table is independent of the outline format and is copied across.
• Layout features survive if the converter copies GSUB, GPOS and GDEF across. Ligatures, kerning pairs, small caps, stylistic sets and old-style figures all live in those tables. A converter that rebuilds a font from outlines alone silently drops every one of them.
• Hinting does not survive. TrueType hinting is bytecode held in fpgm, prep, cvt and in per-glyph instructions; CFF hinting is declared inside the charstrings and interpreted by the rasteriser. Neither translates into the other, so a converted font arrives unhinted and depends on whatever autohinting the renderer applies.
• Variable axes do not survive a conversion that flattens to a single instance. A variable font stores its design space in fvar plus gvar for TrueType outlines or CFF2 for PostScript ones. Export one weight and the other weights are gone, not compressed.
• Vertical metrics can shift. hhea, OS/2 and head each carry ascender, descender and line-gap values, and a rebuilt font that recalculates them instead of copying them will change line spacing in existing layouts.

Do you actually need TTF?

Often not. Windows and macOS have installed both flavours for two decades, so "my system will not take an OTF" is almost never the real problem. For the web, neither raw format is the right answer: serve WOFF2 and keep the desktop file as the source. The conversions that genuinely need glyf outlines are narrower than the search volume suggests.

• Android resource pipelines and some game engines that only parse glyf.
• Embedded and industrial renderers, label printers and older firmware font loaders.
• Editors and plugins that read TrueType outlines only, including a number of vector and CNC toolchains.
• Hinting work, since TrueType bytecode hinting has no CFF equivalent to edit.

Related font conversions

• TTF to WOFF2 for the file you should be serving to browsers.
• TTF to WOFF for the older fallback source.
• WOFF to TTF and WOFF2 to TTF for going the other way.
• Font to Base64 to inline a small face directly into CSS.
• Font availability checker to see which faces a visitor already has locally.
• Format hubs: TTF, OTF, WOFF and WOFF2.