PERF

Use PERF to see how fast and how stable a page feels when it loads.

PERF overview

PERF is the Lighthouse Performance score, from 0 to 100. It’s a lab measurement: the page is loaded in a controlled mobile environment rather than being sampled from real visitors, so the number is comparable from one run to the next.

Like SRPS+, it exists only after a deep audit of that page. You’ll find it in the page header next to SRPS+, and broken down metric by metric in the Mobile (lab) card further down the page audit.

PERF also feeds into SRPS+ as its performance ingredient — so improving speed lifts both numbers.

What it measures

Three things, each with its own row in the card: how long the main content takes to appear (LCP), how long the page is blocked before it responds to input (TBT), and how much the layout shifts while it loads (CLS). Additional lab metrics sit under Other lab metrics.

Each row shows the measured value, the threshold it’s judged against, and a status of Good, Needs work or Poor. In the bars, the dark-green range is the one that scores a full 100 points.

How to read it

The PERF ring uses Lighthouse’s own bands, which are wider than the ones on SRPS and SRPS+: green from 90 up, amber from 50 to 89, red below 50. The same 90–100 / 50–89 / 0–49 legend appears under the card.

Compare runs rather than obsessing over a single number — a lab measurement varies a little between runs even when nothing has changed. A drop of two points is noise; a drop of twenty is a change on the page.

Occasionally a value is marked as a fallback measurement. That means Lighthouse couldn’t complete its normal run, and the value isn’t comparable to the standard thresholds.

What to do when it’s low

Performance fixes are site-wide work, not per-check tweaks, so this page routes rather than instructs.

1. Read the three rows in the Mobile (lab) card to see which of load, interactivity or stability is the problem — they have completely different causes. See Page audit.
2. Hand the specifics to whoever maintains the site. Where the audit found something concrete and fixable, it appears as a technical recommendation with steps. See Technical.
3. Re-run the deep audit for the page to see the new number. Each run uses one unit of your monthly deep-audit quota.

What it does not mean

It isn’t what your visitors experience. PERF is a lab measurement — one page, one simulated mobile device, one moment. Real visitors are on different networks and devices, and their experience can be better or worse than this number suggests.

It doesn’t predict whether AI cites you. Speed is one ingredient of SRPS+ and nothing more. A page that loads instantly and says nothing useful stays uncited.

Its colours don’t line up with the other two scores. PERF uses Lighthouse’s own bands, which are wider than the ones on SRPS and SRPS+. An amber PERF and an amber SRPS are not the same distance from good, so don’t compare the rings at a glance.

A few points of movement is noise. Lab runs vary. Look for changes of a size that a person could have caused.

It isn’t a Google ranking signal readout. Core Web Vitals matter to search, but this is a lab summary in Suparanku, not a report on how Google is treating your site.