Free online OTC to WOFF converter

A program or browser may require WOFF instead of an OpenType Collection, especially when publishing a font for web use. Converting the collection also lets you distribute individual font faces rather than one desktop-oriented package.

What the OTC format is

OTC is the filename extension commonly used for an OpenType Collection, a container holding multiple OpenType fonts that share tables such as glyph data, metrics, or hinting information. Font editors and font-build systems that support collections create OTC files; they are also encountered in operating-system font packages and large typeface families such as CJK fonts.

An OTC can contain several families, weights, styles, or language-specific faces. It may use TrueType outlines or CFF/CFF2 outlines, depending on how the fonts were built.

What the WOFF format is

WOFF is a webfont container designed for use with CSS @font-face. It packages one OpenType font with compressed table data and metadata, reducing transfer size while retaining the font’s outlines, metrics, and layout tables.

Unlike OTC, WOFF stores a single font face. A collection containing six faces therefore normally produces six WOFF files. WOFF is supported by modern browsers, although WOFF2 is usually preferred for new websites when the target environment supports it.

How to actually convert OTC to WOFF

Using the online converter

1. Open the free converter on 101convert.com.
2. Upload the .otc file and select WOFF as the output format.
3. Start the conversion and download the generated WOFF file or files.
4. If the collection contains multiple faces, check that each required family, weight, and style was exported before adding them to a website.

Using fontTools locally

fontTools is the practical desktop and command-line option because it can read OpenType Collections and write WOFF files. Install it with:

python -m pip install fonttools

Save the following as otc_to_woff.py:

import sys
from pathlib import Path
from fontTools.ttLib import TTCollection

source = Path(sys.argv[1])
out = Path(sys.argv[2])
out.mkdir(parents=True, exist_ok=True)

collection = TTCollection(str(source))
for index, font in enumerate(collection.fonts):
    family = font['name'].getDebugName(1) or 'font-%d' % index
    safe = ''.join(c if c.isalnum() or c in '-_' else '_' for c in family)
    font.flavor = 'woff'
    font.save(out / ('%02d-%s.woff' % (index, safe)))

Run it by supplying the OTC filename and an output directory:

python otc_to_woff.py fonts.otc woff-output

The script writes one WOFF per face. Review the generated names and inspect each font’s family, subfamily, weight, and style metadata before referencing it in CSS.

Quality, compatibility, and limitations

• There is no single WOFF equivalent for an OTC collection; every contained face must be exported separately.
• WOFF conversion normally preserves glyph outlines and OpenType shaping tables, but it does not fix malformed source fonts, incorrect naming records, or missing Unicode coverage.
• Use the correct CSS declarations for each exported face, including matching font-family, font-weight, font-style, and the WOFF MIME type font/woff.
• Check the font license before serving the files publicly. A license allowing desktop installation does not necessarily allow web embedding.
• For new browser deployments, generating WOFF2 as an additional format can reduce downloads further; retain WOFF only when older browser compatibility requires it.