Web Performance Glossary

Every number in your report maps to something a real person experiences — a page that loads slowly, a button that feels stuck, content that jumps around. These are the metrics that measure those moments.

Core Web Vitals

LCPUnder 2.5s

Largest Contentful Paint

When the biggest visible element on the page finishes loading.

Good ≤ 2.5s

Needs work 2.5–4s

Poor > 4s

CLSUnder 0.1

Cumulative Layout Shift

How much content jumps around during loading.

Good ≤ 0.1

Needs work 0.1–0.25

Poor > 0.25

INPUnder 200ms

Interaction to Next Paint

How quickly the page responds to taps and clicks.

Good ≤ 200ms

Needs work 200–500ms

Poor > 500ms

CWVAll three passing

Core Web Vitals

The three metrics Google uses for ranking: LCP, INP, CLS.

Other metrics

TTFBUnder 800ms

Time to First Byte

How long the server takes to start responding.

Good ≤ 800ms

Needs work 800ms–1.8s

Poor > 1.8s

FCPUnder 1.8s

First Contentful Paint

When the first text or image appears.

Good ≤ 1.8s

Needs work 1.8–3s

Poor > 3s

TBTUnder 200ms

Total Blocking Time

How long scripts freeze the browser (lab only).

Good ≤ 200ms

Needs work 200–600ms

Poor > 600ms

SIUnder 3.4s

Speed Index

How quickly visible content fills the screen.

Good ≤ 3.4s

Needs work 3.4–5.8s

Poor > 5.8s

TTIUnder 3.8s

Time to Interactive

When the page becomes fully usable.

Good ≤ 3.8s

Needs work 3.8–7.3s

Poor > 7.3s