Unused CSS bytes and the Core Web Vitals
24.7% of audited sites (50,304) parse over 600 KB of unused CSS rules before first paint, passing LCP at 71% (1.9s median) compared with 88% (1.3s median) under 140 KB.
25.3% of sites use under 140 KB of unused CSS unused CSS bytes, and 88% of those sites have a good LCP, against 82% of all sites.
LCP pass rate
Sites with under 140 KB of unused CSS unused CSS bytes have a good LCP most often: 88%, against 82% of all sites. Sites with over 600 KB of unused CSS unused CSS have it least often, at 71%.
Unused CSS bytes usage
300 to 600 KB of unused CSS is the most used: 26.0% of sites. Under 140 KB of unused CSS is 25.3% of sites.
The four LCP phases
Across the four LCP sub-parts in Chrome's field data, the largest gap between under 140 KB of unused CSS and over 600 KB of unused CSS sits in time to first byte (TTFB): 514 ms median for under 140 KB of unused CSS against 861 ms for over 600 KB of unused CSS. Overall median field LCP is 1.3s for under 140 KB of unused CSS (TTFB 514 ms, load delay 278 ms, load duration 141 ms, render delay 216 ms) versus 1.9s for over 600 KB of unused CSS.
Understanding unused CSS bytes
Why unused CSS slows both network transfer and style calculation
Browsers must match every selector in the CSSOM against the DOM tree during layout and style recalculation. Across 51,452 sites (25.3%) with under 140 KB of unused CSS, 88% pass field LCP at a 1.3s median, whereas the 24.7% (50,304) over 600 KB drop to 71% good LCP (1.9s median).
Compile per-template CSS or run PurgeCSS/Tailwind content scanning so pages do not block first paint on hundreds of kilobytes of unreferenced selectors. Across all audited sites, 25.3% stay under 140 KB of unused CSS (88% good LCP, 1.3s median) versus 24.7% above 600 KB (71% good LCP, 1.9s median).
How unused CSS bytes plays out per platform
What the field data shows when you isolate a single CMS or framework.
WordPress 65,482 sites 38% of WordPress sites load over 600 KB of unused CSS (59% vs 85% good LCP under 140 KB).
Across WordPress sites, 38% have over 600 KB of unused CSS (59% good LCP, 2.2s median) compared with 85% (1.5s median) under 140 KB.
Shopify 8,568 sites 58% of Shopify stores have under 300 KB of unused CSS.
Across Shopify storefronts, 20% have under 140 KB of unused CSS (97% LCP pass rate, 1.1s median) and 38% have 140 to 300 KB (97%), compared with 88% above 600 KB.
React 9,567 sites React sites with over 600 KB of unused CSS pass LCP 27 points less often than sites under 140 KB.
Across React sites, 28% have under 140 KB of unused CSS (93% good LCP, 1.1s median) and 22% have over 600 KB of unused styles (66% good LCP, 2.0s median).
Wix 5,825 sites 65% of Wix sites have under 300 KB of unused CSS rules.
Across Wix sites, 33% load under 140 KB of unused CSS (96% LCP pass rate, 995ms median) and 31% load 140 to 300 KB (96%), compared with 88% on the 11% above 600 KB.
By Arjen Karel · 210,902 crawled sites (126,761 with phone Chrome field data, 203,327 sites with unused CSS bytes, October 2026). How we measured.