HTML document size and the Core Web Vitals
35.3% of audited sites (72,808) ship an initial HTML document under 14 KB and reach 87% good LCP (1.3s median), compared to 76% good LCP (1.8s median) on the 25.4% shipping 30 to 75 KB of HTML.
35.3% of sites use under 14 KB of HTML initial HTML document size, and 87% of those sites have a good LCP, against 82% of all sites.
28.2% of sites use 14 to 30 KB of HTML initial HTML document size, and 95% of those sites have a good INP, against 92% of all sites.
Core Web Vitals pass rate
Sites with under 14 KB of HTML initial HTML document size have a good LCP most often: 87%, against 82% of all sites. Sites with 30 to 75 KB of HTML HTML size have it least often, at 76%.
Sites with 14 to 30 KB of HTML initial HTML document size have a good INP most often: 95%, against 92% of all sites. Sites with under 14 KB of HTML HTML size have it least often, at 89%.
Initial HTML document size usage
Under 14 KB of HTML is the most used: 35.3% of sites.
LCP phase breakdown by initial HTML document size
Across the four LCP sub-parts in Chrome's field data, the largest gap between under 14 KB of HTML and 30 to 75 KB of HTML sits in time to first byte (TTFB): 521 ms median for under 14 KB of HTML against 762 ms for 30 to 75 KB of HTML. Overall median field LCP is 1.3s for under 14 KB of HTML (TTFB 521 ms, load delay 268 ms, load duration 131 ms, render delay 214 ms) versus 1.7s for 30 to 75 KB of HTML.
Across the four LCP sub-parts in Chrome's field data, the largest gap between under 14 KB of HTML and 30 to 75 KB of HTML sits in time to first byte (TTFB): 521 ms median for under 14 KB of HTML against 762 ms for 30 to 75 KB of HTML. Overall median field LCP is 1.3s for under 14 KB of HTML (TTFB 521 ms, load delay 268 ms, load duration 131 ms, render delay 214 ms) versus 1.7s for 30 to 75 KB of HTML.
Understanding initial HTML document size
Why the 14 KB initial TCP congestion window sets the pace for LCP discovery
A new TCP connection transfers roughly 14 KB (10 segments) in its first round-trip before waiting for a client ACK. Across 72,808 sites (35.3%) whose HTML fits under 14 KB, 87% achieve good LCP (1.3s median, 521 ms TTFB). Sites between 14 and 30 KB (28.2%) record 82% good LCP (1.6s median), while pages bloating to 30 to 75 KB (25.4%) drop to 76% good LCP (1.8s median) and pages over 75 KB (11.1%) sit at 78% good LCP (1.7s median).
Place <meta charset>, viewport, and <link rel="preload"> for the LCP image at the very top of <head> within the first 14 KB, and trim oversized inline CSS blocks or serialized SSR JSON payloads. Across all audited sites, 35.3% ship under 14 KB (87% good LCP) while 25.4% ship 30 to 75 KB (76% good LCP).
How initial HTML document size plays out per platform
What the field data shows when you isolate a single CMS or framework.
WordPress 65,509 sites WordPress pages over 75 KB HTML (10.9%) pass LCP at 59% vs 82% under 14 KB.
Across 65,509 WordPress sites, 11.8% ship HTML under 14 KB (82% good LCP, 1.6s median), 39.6% ship 14 to 30 KB (73% good LCP), 37.8% ship 30 to 75 KB (65% good LCP), and 10.9% exceed 75 KB (59% good LCP).
Shopify 8,573 stores 89% of Shopify stores ship over 30 KB of HTML (96% good LCP at 30 to 75 KB vs 92% over 75 KB).
Across 8,573 Shopify storefronts, 63.2% transfer 30 to 75 KB of HTML (96% good LCP, 1.3s median) and 25.8% exceed 75 KB (92% good LCP, 1.6s median).
React & Next.js 9,570 sites 67.7% of React & Next.js sites ship over 75 KB of HTML (90% good LCP).
Across React sites, 67.7% transfer over 75 KB of initial HTML (90% good LCP) and 16.9% transfer 30 to 75 KB (65% good LCP).
By Arjen Karel · 210,902 crawled sites (126,761 with phone Chrome field data, 206,244 sites with initial HTML document size, October 2026). How we measured.