Core Web Vitals
Core Web Vitals are three specific measurements Google uses to judge how your website feels to visitors. Not how it looks, not what content it has — how it feels to use.
| Metric | Question it answers | Good score |
|---|---|---|
| LCP (Largest Contentful Paint) | How long until main content appears? | Under 2.5 seconds |
| INP (Interaction to Next Paint) | How long until the page responds when I click? | Under 200ms |
| CLS (Cumulative Layout Shift) | Does stuff jump around while loading? | Under 0.1 |
They're a ranking factor in search, but more importantly, they measure real user experience problems. A slow, janky site loses visitors and conversions whether Google measures it or not. Google uses these as ranking signals — in competitive niches where multiple pages have equally good content, Core Web Vitals can be the tiebreaker.
This guide explains what each metric means, what causes problems, and how to fix them. For the broader context of performance monitoring, start with the pillar page.
LCP: Loading speed
What it measures: Time from page request to when the largest content element is visible. Usually your hero image, main heading, or primary text block.
Why it matters: If your page takes 5 seconds to show content, visitors assume it's broken and leave. LCP correlates directly with bounce rate.
Common causes:
- Large, uncompressed images
- Slow server response time
- Render-blocking CSS and JavaScript
- Web fonts that delay text display
Quick fixes:
- Compress images and use WebP/AVIF formats
- Upgrade from cheap shared hosting
- Defer non-critical JavaScript with
asyncordefer - Preload your largest image
INP: Responsiveness
What it measures: The delay between user interaction (click, tap, keypress) and visible response. INP replaced First Input Delay (FID) in March 2024 and measures all interactions throughout the session, not just the first one.
Why it matters: When you click a button and nothing happens for half a second, you click again. The page feels broken even if it's technically working. This directly causes rage clicks and user frustration.
Common causes:
- Heavy JavaScript execution blocking the main thread
- Long-running tasks (over 50ms)
- Too many event handlers competing for resources
- Third-party scripts (analytics, chat widgets, ads)
Quick fixes:
- Remove unnecessary JavaScript
- Lazy load heavy features
- Audit third-party scripts for main thread blocking
- Delay non-essential scripts until after page is interactive
- Break long tasks into smaller chunks using
requestIdleCallbackorsetTimeout
CLS: Visual stability
What it measures: How much the page layout shifts unexpectedly while loading. Every time an element moves after it's already visible, that's a layout shift.
Why it matters: You're about to tap a link, an ad loads, the link moves, you tap the ad instead. This is one of the most frustrating web experience problems.
Common causes:
- Images without explicit dimensions
- Ads and embeds that load late
- Dynamic content injected after render
- Web fonts that change text size when they load
Quick fixes:
- Always set
widthandheighton images - Reserve space for ads with
min-heightCSS - Use
font-display: swapfor web fonts - Put dynamic content in fixed-size containers
Measuring your Core Web Vitals
For quick tests: PageSpeed Insights shows both lab data (simulated) and field data (real users). Field data is what matters for SEO.
For real data: Google Search Console → Experience → Core Web Vitals. This shows how actual visitors experience your site over the past 28 days.
For continuous monitoring: Tools like askbowtie track Core Web Vitals from real user sessions alongside error monitoring, giving you the full picture of site health. This is the most valuable data because it reflects actual user experience, not lab conditions.
How much do they affect rankings?
Honestly? Less than SEO articles imply.
Content relevance, backlinks, and topical authority still matter far more. A page with poor Core Web Vitals but excellent content will outrank a page with perfect vitals and thin content.
Google's own documentation calls Core Web Vitals a "tiebreaker" signal — when two pages are otherwise equal, the one with better performance gets the edge. But pages are rarely equal in the factors that matter more.
| Ranking factor | Relative importance |
|---|---|
| Content relevance | High |
| Backlink quality | High |
| Topical authority | High |
| Core Web Vitals | Moderate (tiebreaker) |
| Page speed in isolation | Low |
The bigger reason to care isn't SEO — it's conversions. Fix Core Web Vitals and you're fixing real problems that lose visitors, regardless of rankings. A page that loads in 1 second converts better than one that loads in 4 seconds. That's not about Google — that's about users leaving before they see your content.
Core Web Vitals checklist
Before considering Core Web Vitals optimized:
- LCP under 2.5 seconds for 75th percentile users
- INP under 200ms for 75th percentile users
- CLS under 0.1 for 75th percentile users
- All images have explicit width and height
- Largest image is preloaded
- Non-critical JavaScript is deferred
- Third-party scripts audited for performance impact
- Ad containers have reserved space
- Web fonts use font-display: swap
- Search Console shows "Good" for mobile and desktop
Related pages
Parent: Performance & Uptime — Monitor site speed, Core Web Vitals, and uptime
Deep dives:
- How to Improve LCP — Fix slow largest contentful paint
- How to Improve INP — Fix unresponsive interactions
- How to Fix Layout Shift — Reduce cumulative layout shift
Related:
- Error Monitoring — Catch JavaScript errors before they affect users
- Conversion Tracking — Connect performance to business outcomes