Largest Contentful Paint (LCP) is one of the metrics tracked in the Performance section of the Lighthouse report. Each metric captures some aspect of page load speed.
Lighthouse displays LCP in seconds:
What LCP measures
LCP measures when the largest content element in the viewport is rendered to the screen. This approximates when the main content of the page is visible to users. See Largest Contentful Paint defined for more details on how LCP is determined.
How Lighthouse determines your LCP score
Lighthouse extracts LCP data from Chrome's tracing tool.
The following table shows how to interpret your LCP score on mobile:
| LCP time (in seconds) |
Color-coding |
|---|---|
| 0-2.5 | Green (fast) |
| 2.5-4 | Orange (moderate) |
| Over 4 | Red (slow) |
The Web Vitals initiative recommends the same thresholds regardless of device for its thresholds, which basically uses the mobile thresholds. However, since Lighthouse is a lab tool, it can be useful to be stricter when testing for faster desktop devices it uses different thresholds.
The following table shows how to interpret your LCP score on desktop:
| LCP time (in seconds) |
Color-coding |
|---|---|
| 0-1.2 | Green (fast) |
| 1.2-2.4 | Orange (moderate) |
| Over 2.4 | Red (slow) |
How to improve your LCP score
If the LCP is an image, the timing can be broken down into four phases. Knowing which phases take the longest can help you optimize your LCP. Lighthouse will display the LCP element along with the phase breakdown in the "Largest Contentful Paint element" diagnostic.
| LCP phase | Description |
|---|---|
| Time to first byte (TTFB) | The time from when the user initiates loading the page until when the browser receives the first byte of the HTML document response. Learn more about TTFB. |
| Load delay | The delta between TTFB and when the browser starts loading the LCP resource. |
| Load time | The time it takes to load the LCP resource itself. |
| Render delay | The delta between when the LCP resource finishes loading until the LCP element is fully rendered. |