The State of Web Vitals

LCP image byte weight on React sites

48.5% of audited sites (3,110) keep their LCP hero image under 40 KB and pass LCP at 89% (1.3s median), whereas the 9.3% shipping hero images over 300 KB drop to 67% (2.1s median).

Field data PhoneDesktopAll Scope All sites October 2026 edition · Phone field outcomes · React sites only
React Scoped to 9,570 sites out of 210,902 analyzed (frameworks) Compare with all sites →

48.5% of React sites use an LCP image under 40 KB LCP image byte weight, and 89% of those sites have a good LCP, against 84% of all React sites.

The State of Web Vitals · October 2026 · React: 9,570 crawled sites · 5,488 with phone field data · 6,415 sites with LCP image byte weightBy Arjen Karel · corewebvitals.io/state-of-cwv
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LCP pass rate

Sites with an LCP image under 40 KB LCP image byte weight have a good LCP most often: 89%, against 84% of all React sites. Sites with an LCP image over 300 KB hero image size have it least often, at 67%.

SitesGood, needs improvement, poor LCPMedian
All React sites5,48884%1.4s
Under 40 KB hero image 48.5%1,76889%1.3s
40 to 100 KB hero image 29.2%1,07689%1.3s
100 to 300 KB hero image 13.0%48573%1.9s
Over 300 KB hero image 9.3%35867%2.1s
GoodNeeds improvementPoorSites: with Chrome field data
The State of Web Vitals · October 2026 · React: 9,570 crawled sites · 5,488 with phone field data · 6,415 sites with LCP image byte weightBy Arjen Karel · corewebvitals.io/state-of-cwv
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LCP image byte weight usage

An LCP image under 40 KB is the most used: 48.5% of React sites.

Under 40 KB hero image 48.5% 40 to 100 KB hero image 29.2% 100 to 300 KB hero image 13.0%
Under 40 KB hero image 48.5% 40 to 100 KB hero image 29.2% 100 to 300 KB hero image 13.0% Over 300 KB hero image 9.3%
The State of Web Vitals · October 2026 · React: 9,570 crawled sites · 5,488 with phone field data · 6,415 sites with LCP image byte weightBy Arjen Karel · corewebvitals.io/state-of-cwv
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The four LCP phases

Across the four LCP sub-parts in Chrome's field data, the largest gap between an LCP image under 40 KB and an LCP image over 300 KB sits in time to first byte (TTFB): 450 ms median for an LCP image under 40 KB against 1046 ms for an LCP image over 300 KB. Overall median field LCP is 1.2s for an LCP image under 40 KB (TTFB 450 ms, load delay 427 ms, load duration 109 ms, render delay 163 ms) versus 2.0s for an LCP image over 300 KB.

Median LCP phase breakdown (Chrome field p75) Load delay Median LCP
React sites with LCP image byte weight 2,916507 ms427 ms427 mslab 434 ms1.4s
100 to 300 KB hero image 397812 ms405 ms240 ms405 mslab 392 ms1.8s
Under 40 KB hero image 1,385450 ms427 ms427 mslab 438 ms1.2s
40 to 100 KB hero image 841458 ms435 ms435 mslab 436 ms1.3s
Over 300 KB hero image 2931046 ms459 ms231 ms240 ms459 mslab 445 ms2.0s
TTFB Resource load delay Resource load time Element render delay
The State of Web Vitals · October 2026 · React: 9,570 crawled sites · 5,488 with phone field data · 6,415 sites with LCP image byte weightBy Arjen Karel · corewebvitals.io/state-of-cwv
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LCP image byte weight per platform

Wix sets the LCP image byte weight to an LCP image under 40 KB on 61% of its sites, and 94% of Wix sites have a good LCP, against 84% of all sites.

PlatformLCP image byte weight on its sitesGood LCP
React sites with LCP image byte weight 6,415 sitesUnder 40 KB hero image 48%40 to 100 KB hero image 29%100 to 300 KB hero image 13%84%
Wix 4,134 sitesUnder 40 KB hero image 61%40 to 100 KB hero image 33%94%
WordPress 1,701 sitesOver 300 KB hero image 30%100 to 300 KB hero image 25%40 to 100 KB hero image 23%Under 40 KB hero image 22%63%
Under 40 KB hero image 40 to 100 KB hero image 100 to 300 KB hero image Over 300 KB hero image
The State of Web Vitals · October 2026 · React: 9,570 crawled sites · 5,488 with phone field data · 6,415 sites with LCP image byte weightBy Arjen Karel · corewebvitals.io/state-of-cwv
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LCP image byte weight or the platform

Does the platform explain the LCP image byte weight difference?

On Wix, 94% of sites with an LCP image under 40 KB LCP image byte weight have a good LCP, against 96% of Wix sites with an LCP image between 40 and 100 KB. Within Wix, sites with an LCP image under 40 KB and an LCP image between 40 and 100 KB have a good LCP about equally often. On WordPress, 64% of sites with an LCP image under 40 KB LCP image byte weight have a good LCP, against 67% of WordPress sites with an LCP image between 40 and 100 KB. Within WordPress, sites with an LCP image under 40 KB and an LCP image between 40 and 100 KB have a good LCP about equally often.

How intrinsic versus rendered megapixels waste hero bandwidth

The median LCP image is 0.23 intrinsic megapixels rendered into a 0.12 megapixel slot. Serving unresized desktop banners to mobile viewports inflates hero transfer bytes and extends LCP load duration. Across 3,110 sites (48.5%) with a hero image under 40 KB, 89% pass field LCP (1.3s median), dropping to 67% (2.1s median) on the 9.3% (597) exceeding 300 KB.

The State of Web Vitals · October 2026 · React: 9,570 crawled sites · 5,488 with phone field data · 6,415 sites with LCP image byte weightBy Arjen Karel · corewebvitals.io/state-of-cwv
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Understanding LCP image byte weight

Compress hero images below 100 KB using AVIF or WebP and serve responsive srcset widths matched to the rendered viewport slot. Across all audited sites, 48.5% keep the hero image under 40 KB (89% good LCP, 1.3s median) versus 9.3% above 300 KB (67% good LCP, 2.1s median).

Go fix it Optimize the LCP image → LCP: resource load duration → Optimize images for Core Web Vitals →
The State of Web Vitals · October 2026 · React: 9,570 crawled sites · 5,488 with phone field data · 6,415 sites with LCP image byte weightBy Arjen Karel · corewebvitals.io/state-of-cwv
Related signals LCP loading attribute → LCP element type → LCP responsive markup → LCP discovery → By Arjen Karel · 9,570 crawled React sites (5,488 with phone Chrome field data, 6,415 sites with LCP image byte weight, October 2026) · How we measured