Web Performance Glossary

Core Web Vitals

What is LCP?

Largest Contentful Paint measures how long it takes for the main visible content to appear. For most pages, that is a hero image, heading, product photo, or large text block.

Plain-English version

When the biggest visible element on the page finishes loading.

Target

Under 2.5s

LCP thresholds

Use thresholds as a triage tool. Field data matters most when there is enough real Chrome traffic for the page.

Good

≤ 2.5s

Needs work

2.5–4s

Poor

> 4s

Why it matters

What a visitor feels when LCP is bad.

Why LCP matters

LCP is the clearest loading metric for visitors. A page can feel slow even when the Lighthouse score looks fine if the main content appears late on real mobile connections.

What a poor result usually means

A poor LCP usually means the browser discovers the main image too late, waits on render-blocking CSS, receives a slow server response, or downloads too much before it can paint the important content.

What to fix first

Do not chase the score. Fix the bottleneck.

The right fix depends on the metric, the page template, and whether the issue appears in real visitor data.

  1. Identify the LCP element on mobile and desktop.
  2. Preload or prioritize the hero image when it is the LCP element.
  3. Inline critical CSS and defer non-critical styles.
  4. Reduce server response time and unnecessary redirects.
  5. Compress, resize, and serve the LCP image in a modern format.

How nimo helps

Ask nimo: “Why is my LCP slow and how do I fix it?

nimo compares real Chrome field data with Lighthouse diagnostics so you can see whether LCP is a visitor problem, a lab-only warning, or both.

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