Lighthouse Performance Score
How the Lighthouse Score Is Built
The Lighthouse performance score is a number from 0 to 100 that summarizes how a page performed in one simulated test. Lighthouse is an open source auditing tool built into Chrome DevTools, and it also powers the lab section of PageSpeed Insights.
The score is not a simple average of raw times. Lighthouse converts each metric's measured value into a score from 0 to 100 using a curve, then takes a weighted average of those scores. The metrics are a small set chosen to represent different parts of loading. In recent versions they include First Contentful Paint, Speed Index, Largest Contentful Paint, Total Blocking Time and Cumulative Layout Shift. Because the weights and curves are updated over time, scores from different Lighthouse versions may not be directly comparable.
Why the Score Changes Between Runs
Lighthouse runs a simulation of one page load, so results vary. Network timing, server response, background work in the browser and the load on the test machine can all shift the numbers. A change of several points between two runs on the same unchanged page is common and does not necessarily mean anything happened to the page.
Scores also depend on the test settings. Lighthouse emulates a mid-range mobile device on a throttled connection by default, and desktop runs use different settings that usually produce higher scores. Scores from different tools may also differ for the same page for this reason.
For a more reliable comparison, run several tests under the same settings and look at the trend rather than a single result. Metrics such as Speed Index can be read in the same way.
Why 100 Is Not the Goal
A score of 100 means every measured metric landed in the best part of its curve during that one test. It does not mean the page is ideal for visitors. Some pages cannot reach it without removing features people need, such as an interactive map, a video player or a live chat tool. Lighthouse also cannot judge the quality of the content, or whether the page persuades visitors to act.
A more practical goal is a page that stays in the good range for the metrics that matter to its visitors, measured over time. Real-user data, described in the field data article, often shows that more clearly than a single lab score.
Frequently asked questions
What is a good Lighthouse performance score?
Lighthouse groups scores into three ranges. Scores from 90 to 100 are shown as good, 50 to 89 as needing improvement, and 0 to 49 as poor. These ranges are guidelines for a single test rather than a pass or fail mark. A page should be judged over several runs and checked against real visitor data.
Does a high Lighthouse score improve search rankings?
Not on its own. The score is a lab measurement, and search systems use a mix of signals of which speed is only one part. Questions about rankings are covered in the SEO guides, while this article only explains what the number measures.