Layout shift causes (CLS attribution) and Cumulative Layout Shift
Element box growth (78.5%), sibling displacement (34.7%), web font reflow (23.9%), unsized media (3.9%), and late embed growth (0.5%) across 135,809 sites with recorded layout shifts.
23.9% of sites use web font reflow layout shift causes, and 76% of those sites have a good CLS, against 78% of all sites.
CLS pass rate
Sites with web font reflow layout shift causes have a good CLS most often: 76%, against 78% of all sites. Sites with late embed growth shift causes have it least often, at 65%.
Layout shift causes usage
Element box growth is the most used: 78.5% of sites. Web font reflow is 23.9% of sites.
Understanding layout shift causes
How different DOM mutations translate into field CLS failures
Not all lab layout shifts hurt real users equally. Sites whose shifts come from web font swaps (23.9%) pass field CLS 76% of the time because line-height adjustments are small. Element box growth (78.5%, 73% good CLS) and displaced siblings (34.7%, 73% good CLS) cause moderate drops, while late iframe and embed growth (0.5%) pulls field CLS down to 65% (median CLS 0.07).
Eliminate late embed and banner growth first by reserving min-height containers for ad slots, promo bars, and third-party widgets. While 78.5% of shifting sites see element box growth (73% good CLS) and 23.9% see font swap reflow (76% good CLS), sites with unreserved iframe or embed growth (0.5%) pass field CLS only 65% of the time.
How layout shift causes plays out per platform
What the field data shows when you isolate a single CMS or framework.
WordPress 46,752 sites On WordPress sites with lab layout shifts, embed_grow sites pass field CLS at 56% vs 76% on font_text sites.
Across 46,752 WordPress sites with lab layout shifts, 78.5% record element box growth (73% good field CLS), 24.2% record web font reflow (76% good CLS), and 0.7% record embed_grow (56% good CLS).
Shopify 5,622 stores Among shifting Shopify stores, 79.7% record box growth (81% good CLS) and 35.8% record sibling displacement.
Across 5,622 Shopify storefronts with lab layout shifts, 79.7% record element box growth (81% good field CLS) and 35.8% record sibling displacement (81% good CLS).
React & Next.js 4,060 sites Among shifting React sites, unsized_media sites pass field CLS at 46% and displaced sites at 72%.
Across 4,060 React sites that record a lab layout shift, 75.8% record box growth (67% good CLS), 36.2% record sibling displacement (72% good CLS), and 2.3% record unsized media shifts (46% good CLS).
By Arjen Karel · 212,308 crawled sites (70,213 with desktop Chrome field data, 135,809 sites with layout shift causes, October 2026). How we measured.