How fast should your website be? A plain-English guide to Core Web Vitals

Speed is a business problem, not just a technical one

A slow site loses visitors before they ever see what you offer. Google also uses page experience as a ranking signal, so speed affects both how many people find you and how many stay.

Google measures this through three metrics called Core Web Vitals. They sound technical, but each one maps to something a real person notices.

The three metrics

Largest Contentful Paint (LCP) — "when does the main thing appear?"

This measures how long until the biggest visible element finishes loading. Usually that is a hero image or headline.

• Good: under 2.5 seconds
• Needs work: 2.5 to 4 seconds
• Poor: over 4 seconds

The most common causes of a bad LCP are oversized images and slow server response.

Interaction to Next Paint (INP) — "does it respond when I tap?"

This measures the delay between a visitor interacting and the page visibly responding.

• Good: under 200 milliseconds
• Needs work: 200 to 500 milliseconds
• Poor: over 500 milliseconds

Bad INP usually means too much JavaScript running at once, often from tracking scripts, chat widgets and pop-up tools stacked on top of each other.

Cumulative Layout Shift (CLS) — "did the page jump while I was reading?"

You have felt this one. You go to tap a button, an ad loads above it, everything shifts, and you tap the wrong thing.

• Good: under 0.1
• Needs work: 0.1 to 0.25
• Poor: over 0.25

The usual cause is images or embeds without reserved space, so the browser does not know how much room to leave.

How to check your own site

Two free tools:

• PageSpeed Insights — paste in a URL and get both lab results and real-world data from actual Chrome users.
• Google Search Console — the Core Web Vitals report shows how your real visitors experience the site over time.

Prefer the real-world numbers. A test run on a fast connection can look great while your actual customers on mobile data have a very different experience.

The fixes that usually matter most

1. Compress and resize images. This is the biggest win on most sites. Serve modern formats and never ship a 3000px image into a 600px slot.
2. Always set width and height on images. This alone fixes most layout shift.
3. Audit your third-party scripts. Every analytics tool, chat widget and pixel costs you speed. Keep the ones you actually use.
4. Load fonts sensibly. Use a fallback so text is readable while your font loads.
5. Use decent hosting. If your server takes a second to respond, no amount of front-end work fixes it.

A realistic target

You do not need a perfect score. Getting all three metrics into the "good" band puts you ahead of most sites and, more importantly, gives visitors a site that feels quick.

Chasing 100 out of 100 usually costs far more effort than it returns. Fix the images, trim the scripts, reserve space for media, and you will have captured most of the benefit.