How to use the web font subset savings calculator
A web font that ships a full glyph set can run from a few hundred KB to over 1 MB per file. Subsetting keeps only the glyphs you actually use, but unless you check the reduction as a number you cannot tell whether the build worked. This calculator takes the file size and glyph count before and after subsetting and reports the saving, the saving rate, bytes per glyph and the total saving across every weight you ship.
The arithmetic is plain. The saving is the size before minus the size after, and the rate is that difference divided by the size before, as a percentage. Bytes per glyph multiplies the file size by 1,024 and divides by the glyph count. Sizes use 1 KB = 1,024 bytes, and the page was written as of October 2026.
The tool does not publish compression rates by format. WOFF2 is known to be smaller than TTF, but how much smaller depends on the glyph set and hinting inside a given font, and no authoritative table exists. That is why it never estimates the size after subsetting and asks for the real build output instead. Cache hit rates, HTTP compression and font loading strategy are also left out, so confirm the final numbers against real transfer sizes in your network panel.
Frequently Asked Questions
No. Removing the same glyphs gives different results depending on format, hinting and compression, and there is no authoritative compression table, so the tool reads the real size of the file you built and reports only the difference.
Glyphs carry different numbers of outline points, so they cost different numbers of bytes, and shared data such as kerning and hinting stays in the file even after glyphs are dropped. That is why the two rates are shown separately.
The saving across all files is multiplied by the monthly loads you entered. Cache hit rates are not included, so real savings are smaller when caching works well. Leave the field blank to skip it.