Image dimension sizing (width/height, aspect-ratio) and Cumulative Layout Shift
Explicit width and height attributes (72.0%), CSS aspect-ratio (3.5%), and unsized <img> tags (82.5%): how reserving image boxes moves Cumulative Layout Shift.
72.0% of sites use explicit width and height image dimension sizing, and 79% of those sites have a good CLS, against 78% of all sites.
CLS pass rate
Sites with explicit width and height image dimension sizing have a good CLS most often: 79%, against 78% of all sites. Sites with CSS aspect-ratio image dimensions have it least often, at 75%.
Image dimension sizing usage
Unsized <img> is the most used: 82.5% of sites. Explicit width and height is 72.0% of sites.
Understanding image dimension sizing
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, 72.0% of sites size images with HTML width and height (79% good CLS), while 82.5% still include at least one unsized <img> (77% good CLS) and 3.5% use CSS aspect-ratio without HTML attributes (75% good CLS).
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, 72.0% include explicitly sized images (79% good CLS), whereas 82.5% still ship at least one unsized image (77% good CLS) and 3.5% rely solely on CSS aspect-ratio (75% good CLS).
How image dimension sizing plays out per platform
What the field data shows when you isolate a single CMS or framework.
WordPress 65,177 sites WordPress sets width and height on 92.2% of sites, while 74.4% also have unsized images.
WordPress core adds width and height attributes to media library images with wp_img_tag_add_width_and_height_attr(). Across WordPress, 92.2% of sites include explicitly sized images (77% good CLS) and 74.4% include at least one unsized <img> (77% good CLS).
React & Next.js 9,502 sites React sites with HTML width/height (88.3%) pass CLS 17 points more often than sites with CSS-only aspect-ratio (5.0%).
Next.js <Image> requires width and height props unless fill is set. Across React sites, 88.3% include HTML width and height attributes (82% good CLS) and 5.0% use CSS aspect-ratio (65% good CLS).
By Arjen Karel · 210,902 crawled sites (69,745 with desktop Chrome field data, 193,893 sites with image dimension sizing, October 2026). How we measured.