View Metric Subparts

---

Subparts break metrics into smaller components to help teams prioritise the correct causes for high metric values.

Display subpart metrics

1. Navigate to CrUX → LCP page.
2. Select grouping by Metric subparts in the upper right hand side corner.

Largest Contentful Paint Subparts

Subparts are only measured for image resources classified as Largest Contentful Paint elements (videos and text resources are not evaluated). This data has been added to CrUX API and CrUX History API in February 2025, and is available from that timeframe.

Largest Contentful Paint consists of the following subparts:

Subpart	Definition	Common Issues
Image Render Delay	Time between the browser discoveres the image and when it starts downloading it.	Rendering of the image is blocked by another resource type (JavaScript execution or blocking CSS).
Image Load Duration	Time between the browser starting to fetch the image and completing the download.	The image load is extensive due to large, uncompressed file size, outdated image format, or lack of appropriate responsive image implementation.
Image Load Delay	Time between the image being downloaded and displayed on screen.	Load is delayed due to the browser being unable to locate the image due to image being lazy loaded without appropriate preloading, image being loaded via JavaScript, or other resources having a higher priority.
Time to First Byte	Time between a request for a resource and the first byte arriving to the browser.	The server has a slow response time, unnecessary redirects are adding to the delays, or there’s no CDN in place.