What are LCP, CLS, and INP, and what are good thresholds?

Question

IT Interview Practice · Accepted Answer

**Core Web Vitals** are three field metrics Google uses to score real user experience: **LCP** (loading), **CLS** (visual stability), and **INP** (responsiveness).

## What each one measures

- **LCP — Largest Contentful Paint**: time until the biggest visible element (hero image, headline) is rendered. It answers "did the main content appear fast?"
- **CLS — Cumulative Layout Shift**: how much content jumps around unexpectedly while loading. It answers "did the page stay stable?"
- **INP — Interaction to Next Paint**: how quickly the page responds to taps/clicks/keypresses across the whole visit. It answers "does it feel snappy?" INP replaced FID in March 2024.

## Good thresholds

| Metric | Good | Needs work | Poor |
|--------|------|-----------|------|
| LCP | ≤ 2.5s | ≤ 4.0s | > 4.0s |
| CLS | ≤ 0.1 | ≤ 0.25 | > 0.25 |
| INP | ≤ 200ms | ≤ 500ms | > 500ms |

Google grades at the **75th percentile** of real users — so "good" means 75% of visits hit the target, not just your fast test on a fast laptop.

## Why it matters

Interviewers ask this to check you know the *current* metrics (INP, not FID) and their thresholds. These scores feed Google Search ranking and correlate directly with bounce rate and conversions, so knowing what each measures tells you where to focus a slow page.

Metric	Good	Needs work	Poor
LCP	≤ 2.5s	≤ 4.0s	> 4.0s
CLS	≤ 0.1	≤ 0.25	> 0.25
INP	≤ 200ms	≤ 500ms	> 500ms

What each one measures

Good thresholds

Why it matters

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