# Core Web Vitals

> What each Core Web Vital measures, the difference between lab and field data, and how much of a ranking factor they actually are.

Source: https://netweft.com/glossary/core-web-vitals
Updated: 2026-03-05

**A set of three field-measured metrics Google uses to describe page experience: Largest Contentful Paint for loading, Interaction to Next Paint for responsiveness, and Cumulative Layout Shift for visual stability.**

Three metrics, each measuring a different kind of annoyance.

**Largest Contentful Paint (LCP)** — how long until the biggest thing above the
fold is drawn. This is "did the page appear".

**Interaction to Next Paint (INP)** — how long the page takes to respond
visibly after a user interacts. This is "did the page listen".

**Cumulative Layout Shift (CLS)** — how much the layout moves around after it
first draws. This is "did the page stay still while I was reading it".

**Lab is not field.** A Lighthouse run is a synthetic measurement on one
machine under one network profile. Core Web Vitals as Google uses them are
field data from real visits. A perfect lab score with poor field data usually
means your real users are on worse devices and networks than your test.

**Keep the weighting honest.** These are a real signal and a small one.
Fixing a page that takes six seconds to render is worth doing for its own sake.
Chasing a score from 92 to 96 rarely moves a ranking, and netweft [prices the
per-page performance check at 50 credits](/pricing) partly so that the cost
of chasing it is visible before you start. What that does to a full crawl is
worked through in [what a 500-page crawl costs](/blog/what-a-crawl-costs).