Engineering
Core Web Vitals
Also called
- LCP
- INP
- CLS
Core Web Vitals are three field measurements taken from real visitors rather than a lab: Largest Contentful Paint (how long until the main content is visible), Interaction to Next Paint (how quickly the page responds when someone taps or clicks), and Cumulative Layout Shift (how much the page moves under them while it loads).
They are reported at the 75th percentile, which is the number that matters and the number most teams never look at. An average of 1.2 seconds can hide a quarter of your visitors waiting four. The percentile is deliberate: it describes the experience of the unlucky quarter rather than the comfortable middle.
They are a confirmed input to Google's ranking, but the ranking effect is the smaller half of the argument. The larger half is that they track closely with conversion on mobile, because a visitor who is still looking at a blank screen has not yet decided to stay.
On a mobile-majority site, moving LCP from four seconds to under two typically moves conversion more than any copy change you could make in the same week.
Commonly misunderstood
What people get wrong
The claim
“Our Lighthouse score is 98, so we're fine.”
What is actually true
Lighthouse is a lab test on a simulated device. Core Web Vitals are field data from your actual visitors on their actual phones and networks. The two frequently disagree, and only one of them is what Google uses.
Related terms
Next step
Working through a core web vitals decision?
Tell us the situation. We will give you the tradeoffs as we see them, including when the answer is that you do not need what you are being sold.
No pitch deck. A 30-minute conversation about what you are trying to achieve.