docs/speed/metrics_changelog/2026_02_cls.md
Prior to Chrome 145, the Layout Instability API reported attribution data
(prevRect and currentRect in LayoutShift entries) in physical pixels,
which varied based on the device's devicePixelRatio. Starting in Chrome 145,
these rectangles are now reported in CSS pixels for consistency with other
web platform APIs like getBoundingClientRect().
This change makes layout shift data easier to visualize, debug, and combine across devices and tools, as CSS pixels are the standard unit used throughout the web platform for layout measurements.
The specification change was merged in WICG/layout-instability#125.
The source code changes can be seen in the following CLs:
This change affects the units used to report layout shift attribution data, not the actual CLS score values. The shift scores themselves remain unchanged.
Sites and tools that consume LayoutShift attribution data (primarily Real User
Monitoring and analytics tools) will need to update their processing logic if
they were assuming physical pixels. Tools that visualize layout shifts on top
of page screenshots will need to account for CSS pixels when positioning overlays.
For most use cases, CSS pixels are more intuitive and easier to work with than physical pixels.
Chrome 145 is expected to reach stable users in February 2026.