How to coverage map vs glyph count: different questions, different answers
- Step 1Run both tools — Glyph Count → total glyphs + WOFF2 size projections. Coverage Map → per-block coverage.
- Step 2Compare for the same font — 5,000 glyphs covering Latin Basic 100% + CJK 30% might be the wrong choice if your audience is Chinese. The same 5,000 glyphs covering 100% of CJK + 0% Latin is right for Chinese-only sites.
- Step 3Match against your audience — Combined metrics: glyph count drives bandwidth budget; coverage drives language fitness. Both must match your audience for a font to be appropriate.
Frequently asked questions
Can a font have unused glyphs?+
Yes — many fonts ship glyphs without Unicode codepoints (alternate forms accessible only via OpenType features). These count toward total glyphs but not toward Unicode coverage. The Glyph Count tool shows total; Coverage Map shows Unicode-encoded subset.
Why does coverage matter for performance?+
Subsetting decisions depend on coverage. If a font only covers 30% of CJK Unified Ideographs, subsetting to a CJK target can't recover the missing 70% — pick a different font. Coverage Map is the upfront screen before subsetting.
How accurate is the percentage?+
Counts encoded codepoints versus block size. 100% means every codepoint in the block has a glyph. Lower percentages flag partial coverage — useful but worth digging into which specific codepoints are missing.
Privacy first
Every JAD Font tool runs entirely in your browser using opentype.js and the wawoff2 WASM Brotli encoder. Your fonts never leave your device — verified by zero outbound network requests during processing.