At a glance the headline numbers for Font format mix
Font formats in use: woff2, woff, ttf and friends.
82.2% of font files are WOFF2.
The font format mix mix who uses what, and how stable each group is
Font format mix. On the fleet: 82.2% woff2, 9.7% woff, 6.9% ttf. 84.6% of sites use at least one woff2.
Woff2 leads by count (82.2%) and by bytes (73.8%). computed
Passing CLS per bucket every category and count level at once - color is the pass rate
Each row is a category, each column its own count bucket (few on the left, many on the right); the cell is the share of those sites passing CLS.
Ttf swings the hardest: 85% of sites pass CLS with few, 77% with many. computed
Few vs many - does quantity cost CLS? the pass rate with few vs many of each category
Per category: the pass rate among pages with FEW of it (hollow ring) against pages with MANY (solid dot), worst trend first. Thin buckets are excluded from the endpoints.
More Ttf costs the most: the CLS pass rate falls from 85% with few to 77% with many. computed
Why this matters for the Core Web Vitals, and where to start fixing it
woff2 is the only font format a modern site needs. It compresses tighter than woff and far tighter than ttf or otf, and every current browser supports it. Anything else in the mix is either a legacy fallback nobody downloads or bytes wasted on the wire.
Font bytes sit on the render path. Text either waits for them or reflows when they arrive, so smaller font files shorten that window whatever your font-display strategy is.
How does this affect the Core Web Vitals?
The choice barely moves the LCP: 82% pass at best, 78% at worst. This signal does not separate passing sites from failing ones.
Chrome field data from 94,910 sites, representing millions of real page loads. How we measured.