Unused JavaScript bytes and the Core Web Vitals
25.9% of audited sites (53,454) ship over 1.5 MB of unused JavaScript during initial load, pushing median INP to 117ms (88% good INP) versus 91ms (96% good INP) at 400 to 850 KB.
26.9% of sites use 400 to 850 KB of unused JS unused JavaScript bytes, and 96% of those sites have a good INP, against 92% of all sites.
22.2% of sites use under 400 KB of unused JS unused JavaScript bytes, and 89% of those sites have a good LCP, against 82% of all sites.
Core Web Vitals pass rate
Sites with 400 to 850 KB of unused JS unused JavaScript bytes have a good INP most often: 96%, against 92% of all sites. Sites with over 1.5 MB of unused JS unused JS have it least often, at 88%.
Sites with under 400 KB of unused JS unused JavaScript bytes have a good LCP most often: 89%, against 82% of all sites. Sites with over 1.5 MB of unused JS unused JS have it least often, at 75%.
Unused JavaScript bytes usage
400 to 850 KB of unused JS is the most used: 26.9% of sites.
Understanding unused JavaScript bytes
How dead JavaScript code still blocks the main thread
The browser cannot skip parsing or compiling unused functions inside a downloaded bundle. Across 55,440 sites (26.9%) with 400 to 850 KB of unused JS, 96% pass field INP at an 91ms median, while the 25.9% (53,454) exceeding 1.5 MB of unused JS drop to 88% good INP (117ms median).
Use route-level code splitting and dynamic import() so offscreen modals, checkout flows, and heavy third-party SDKs only load when needed. Across all audited sites, 26.9% ship 400 to 850 KB of unused JS (96% good INP, 91ms median) versus 25.9% above 1.5 MB (88% good INP, 117ms median).
How unused JavaScript bytes plays out per platform
What the field data shows when you isolate a single CMS or framework.
WordPress 65,496 sites 54% of WordPress sites ship over 850 KB of unused JavaScript.
Across WordPress sites, 31% load 850 KB to 1.5 MB of unused scripts and 23% exceed 1.5 MB, with median INP ranging from 84ms under 400 KB unused to 111ms above 1.5 MB.
Shopify 8,572 sites 64% of Shopify stores ship over 1.5 MB of unused JavaScript on load.
Across Shopify storefronts, 64% have over 1.5 MB of unused JS during initial load (91% good INP, 121ms median) compared with 99% (95ms median) at 850 KB to 1.5 MB.
React 9,570 sites 68% of React sites load over 1.5 MB of unexecuted JavaScript code.
Across React sites, 68% have over 1.5 MB of unused JS on initial load (92% INP pass rate, 94ms median) and 25% have 850 KB to 1.5 MB (96%).
Wix 5,825 sites 72% of Wix sites sit in the over 1.5 MB unused JS tier (96% good INP).
Across Wix sites, 72% record over 1.5 MB of unused JS on first load (96% good INP) and 28% record 850 KB to 1.5 MB (97% good INP).
By Arjen Karel · 210,902 crawled sites (126,761 with phone Chrome field data, 206,167 sites with unused JavaScript bytes, October 2026). How we measured.