Core Web Vitals

What Core Web Vitals actually measure

Core Web Vitals are Google’s attempt to reduce “is this page a pleasant experience?” to three numbers a machine can check. Each one covers a different way a page can feel broken:

• Largest Contentful Paint (LCP) — loading. How long until the main content is actually on screen.
• Interaction to Next Paint (INP) — responsiveness. How quickly the page reacts when someone taps or clicks.
• Cumulative Layout Shift (CLS) — visual stability. How much things jump around while loading.

They are deliberately experience-focused rather than technical. A page can have small files and clean code and still fail all three.

The thresholds

Metric	Good	Needs improvement	Poor
LCP	2.5 seconds or less	2.5 – 4.0 seconds	Over 4.0 seconds
INP	200 ms or less	200 – 500 ms	Over 500 ms
CLS	0.1 or less	0.1 – 0.25	Over 0.25

The 75th percentile rule that trips people up

Google does not grade the average visit. It grades the 75th percentile of real visits, measured separately for mobile and desktop.

In plain terms: three out of four visitors must have a good experience before the page counts as passing. One fast test on your office wi-fi proves nothing. The visitor standing in a parking lot on a weak signal is inside the measurement, and on a mobile-heavy local business site that visitor is often the majority.

This is also why a page can pass in Lighthouse and still fail in Google’s eyes. Lighthouse runs a simulated load on your machine. Google grades field data collected from actual Chrome users.

First Input Delay is gone

If a proposal or audit still reports First Input Delay (FID), it is out of date. INP replaced FID as a stable Core Web Vital in 2024.

The distinction matters commercially: FID only measured the delay before the first interaction was handled, which most sites passed easily. INP measures responsiveness across the entire visit, and plenty of sites that scored well on FID fail INP outright.

How much does this actually affect rankings?

Honestly: less than most agencies imply. Core Web Vitals are a real but modest ranking signal, and relevance beats speed nearly every time. A fast page about the wrong thing does not outrank a slow page that answers the question.

The stronger argument is commercial rather than algorithmic. Slow, jumpy pages lose people before they read anything — and on a site where a handful of calls a month covers the cost of the whole thing, that loss is measurable in a way rankings are not.

What usually causes failures

In our experience auditing small business sites, the recurring culprits are:

• Uncompressed hero photos straight off a phone or camera, often several megabytes each
• Page builder plugins loading their entire library on every page
• Third-party embeds — chat widgets, review carousels, tracking scripts — that block rendering
• Images and ads without reserved space, which is nearly always the CLS problem
• Fonts loaded from a third-party server, delaying every piece of text

None of these need a rebuild. Most are fixable in an afternoon once you know which one is responsible.