Image dimension sizing on React sites
Explicit width and height attributes (88.3%), CSS aspect-ratio (5.0%), and unsized <img> tags (75.5%): how reserving image boxes moves Cumulative Layout Shift.
88.3% of React sites use explicit width and height image dimension sizing, and 82% of those sites have a good CLS, against 80% of all React sites.
CLS pass rate
Sites with explicit width and height image dimension sizing have a good CLS most often: 82%, against 80% of all React sites. Sites with CSS aspect-ratio image dimensions have it least often, at 65%.
Image dimension sizing usage
Explicit width and height is the most used: 88.3% of React sites.
Image dimension sizing per platform
Wix sets the image dimension sizing to explicit width and height on 98% of its sites, and 96% of Wix sites have a good CLS, against 80% of all sites.
Wix 5,802 sitesExplicit width & height attributes 98%Unsized <img> (no width/height or aspect-ratio) 71%96%
WordPress 2,334 sitesExplicit width & height attributes 94%Unsized <img> (no width/height or aspect-ratio) 81%75%Image dimension sizing or the platform
Does the platform explain the image dimension sizing difference?
On Wix, 95% of sites with explicit width and height image dimension sizing have a good CLS, against 96% of Wix sites with unsized <img>. Within Wix, sites with explicit width and height and unsized <img> have a good CLS about equally often. On WordPress, 75% of sites with explicit width and height image dimension sizing have a good CLS, against 74% of WordPress sites with unsized <img>. Within WordPress, sites with explicit width and height and unsized <img> have a good CLS about equally often.
How browsers compute intrinsic aspect ratios from HTML width and height
User-agent stylesheets map HTML width and height attributes directly to an internal aspect-ratio property before the image file downloads. Across the web, 88.3% of sites size images with HTML width and height (82% good CLS), while 75.5% still include at least one unsized <img> (78% good CLS) and 5.0% use CSS aspect-ratio without HTML attributes (65% good CLS).
Understanding image dimension sizing
Set explicit width and height attributes on every <img> element so the browser reserves its aspect ratio before stylesheets or image bytes arrive. Across all audited sites, 88.3% include explicitly sized images (82% good CLS), whereas 75.5% still ship at least one unsized image (78% good CLS) and 5.0% rely solely on CSS aspect-ratio (65% good CLS).
By Arjen Karel · 9,570 crawled React sites (1,979 with desktop Chrome field data, 9,502 sites with image dimension sizing, October 2026). How we measured.