Shopify HTML document size and the Core Web Vitals

Sites with under 14 KB of HTML initial HTML document size have a good LCP most often: 99%, against 97% of all Shopify sites. Sites with over 75 KB of HTML HTML size have it least often, at 93%.

Sites with 14 to 30 KB of HTML initial HTML document size have a good INP most often: 100%, against 99% of all Shopify sites. Sites with under 14 KB of HTML HTML size have it least often, at 99%.

30 to 75 KB of HTML is the most used: 63.6% of Shopify sites. Under 14 KB of HTML is 4.4% of Shopify sites.

Across the four LCP sub-parts in Chrome's field data, the largest gap between under 14 KB of HTML and over 75 KB of HTML sits in resource load delay: 634 ms median for under 14 KB of HTML against 735 ms for over 75 KB of HTML. Overall median field LCP is 1.3s for under 14 KB of HTML (TTFB 302 ms, load delay 634 ms, load duration 139 ms, render delay 327 ms) versus 1.5s for over 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 over 75 KB of HTML sits in resource load delay: 634 ms median for under 14 KB of HTML against 735 ms for over 75 KB of HTML. Overall median field LCP is 1.3s for under 14 KB of HTML (TTFB 302 ms, load delay 634 ms, load duration 139 ms, render delay 327 ms) versus 1.5s for over 75 KB of HTML.

On jQuery, 57% of sites use 30 to 75 KB of HTML initial HTML document size, and 95% of jQuery sites have a good LCP, against 97% of all sites. On Vue, 52% of sites use 30 to 75 KB of HTML, and 97% of Vue sites have a good LCP.

On jQuery, 57% of sites use 30 to 75 KB of HTML initial HTML document size, and 99% of jQuery sites have a good INP, against 99% of all sites. On Vue, 52% of sites use 30 to 75 KB of HTML, and 100% of Vue sites have a good INP.

FrameworkInitial HTML document size on its sitesGood LCP

All Shopify sites 8,246 sites30 KB to 75 KB 64%Over 75 KB 26%97%

Vue 933 sites30 KB to 75 KB 52%Over 75 KB 41%97%

jQuery 3,153 sites30 KB to 75 KB 57%Over 75 KB 31%95%

30 KB to 75 KB Over 75 KB 14 KB to 30 KB Under 14 KB (First TCP window)

Does the framework explain the initial HTML document size difference?

On jQuery, 98% of sites with under 14 KB of HTML initial HTML document size have a good LCP, against 98% of jQuery sites with 30 to 75 KB of HTML. Within jQuery, sites with under 14 KB of HTML and 30 to 75 KB of HTML have a good LCP about equally often. On Vue, 99% of sites with 30 to 75 KB of HTML initial HTML document size have a good LCP, against 94% of Vue sites with over 75 KB of HTML. Within Vue, sites with 30 to 75 KB of HTML have a good LCP more often.

On jQuery, 100% of sites with 14 to 30 KB of HTML initial HTML document size have a good INP, against 100% of jQuery sites with 30 to 75 KB of HTML. Within jQuery, sites with 14 to 30 KB of HTML and 30 to 75 KB of HTML have a good INP about equally often. On Vue, 100% of sites with 30 to 75 KB of HTML initial HTML document size have a good INP, against 99% of Vue sites with over 75 KB of HTML. Within Vue, sites with 30 to 75 KB of HTML and over 75 KB of HTML have a good INP about equally often.

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 360 sites (4.4%) whose HTML fits under 14 KB, 99% achieve good LCP (1.3s median, 302 ms TTFB). Sites between 14 and 30 KB (6.4%) record 98% good LCP (1.0s median), while pages bloating to 30 to 75 KB (63.6%) drop to 99% good LCP (1.2s median) and pages over 75 KB (25.6%) sit at 93% good LCP (1.5s median).