Your guide to Core Web Vitals

In the past, page speed was a vague concept. You knew faster was better, but you didn't have a clear scorecard. That changed when Google introduced Core Web Vitals.

If you are a business owner or marketing manager, you don't need to write the code. But you must understand what these metrics measure and how they impact revenue. They are now a critical part of your search engine optimisation (SEO) strategy.

This guide explains the three pillars of Core Web Vitals in plain English, along with the supporting metrics that influence them.

What are Core Web Vitals?

Think of Core Web Vitals (CWV) as a medical checkup for your website. Doctors track blood pressure to judge physical health. Similarly, Google measures three signals to judge page experience health.

Google has explicitly stated that these signals are a ranking factor.

The SEO reality: how much do they matter?

It is important to set expectations. SEO experts view Core Web Vitals as a tie-breaker signal.

While search engine crawlers scan your text to understand relevance, Core Web Vitals measure the actual human experience. If your content is low quality, a fast website won't save you. Content is still king.

However, in competitive markets, competitors often have similar content quality. Core Web Vitals become the tie-breaker. They can decide if you rank #1 or drop to #4.

Beyond SEO, they are critical for conversion. A site that passes Core Web Vitals correlates directly with lower bounce rates and higher conversion rates. Deloitte found that a mere 0.1s improvement in speed resulted in an 8% increase in conversions for retail sites.

The three pillars of page experience

Google looks at three specific metrics. Each measures a different part of the user's struggle (or success) in using your site.

1. LCP (largest contentful paint)

The loading speed metric

• In plain English: How fast does the main part of the page show up?
• The analogy: Imagine walking into a physical store. LCP is the time it takes for the lights to turn on so you can actually see the products. If you walk in and stand in the dark for 4 seconds, you leave.
• What Google measures: It measures the time from a user's click until the largest visible element appears. This is usually the hero image, video poster, or main headline. It is the most accurate measure of perceived loading speed.
• Common culprits:
• Unoptimised images: Uploading a 4MB photo when a 100KB web-optimised image would suffice.
• Slow server response times: Cheap hosting creates lag. If your server is in New York but customers are in Sydney, distance kills your LCP.
• Render-blocking JavaScript: Scripts that force the browser to pause building the visual page to read code.
• The criteria:
• Good: Under 2.5 seconds
• Needs improvement: 2.5s to 4.0s
• Poor: Over 4.0s

2. INP (interaction to next paint)

The interactivity metric (Replaced FID in March 2024)

• In plain English: When a user clicks a button, how fast does the site react?
• The analogy: You are at a restaurant. You wave at a waiter (the click).
• Good INP: The waiter nods immediately, acknowledging you.
• Poor INP: The waiter stares blankly at you for 3 seconds before moving.
• Why it matters: This measures frustration. Users assume the site is broken if a button fails to react instantly.
• This often leads to rage clicking (tapping the same button repeatedly), which confuses the browser further.
• The old metric (FID) only measured the first click. INP tracks every user interaction during the entire visit.
• Common culprits:
• Heavy JavaScript execution: The browser is too busy thinking about code to respond to the user's tap.
• Third-party scripts: Chat widgets, tracking pixels, and social media feeds often load heavy code that clogs the browser's main thread.
• The criteria:
• Good: Under 200 milliseconds
• Needs improvement: 200ms to 500ms
• Poor: Over 500ms

3. CLS (cumulative layout shift)

The visual stability metric

• In plain English: Does the page jump around while it loads?
• The analogy: You are reading a magazine article. Suddenly, an ad loads at the top of the page and pushes the text you were reading down three inches. You lose your place. That is a layout shift.
• The business risk: This is the accidental click metric. High CLS causes accidental clicks. Users often hit the wrong button because the layout shifts just as they tap. This creates a deceptive and poor user experience.
• Common culprits:
• Images without dimensions: Browsers need exact dimensions. If the code lacks width and height data, the browser cannot reserve space for the image.
• Ads and banners: Dynamic ads that inject themselves into the content stream often push content down.
• Web fonts: If a custom font loads slowly, the text might flash or change size when the font finally arrives (FOUT), shifting the layout.
• The criteria:
• Good: Score of less than 0.1
• Needs improvement: 0.1 to 0.25
• Poor: Score above 0.25

Beyond the core: other important metrics

Google uses the three metrics above as its specific Core ranking vitals. However, they are part of a broader group of signals called Page Experience.

The diagnostic metrics (how web developers fix the core)

You might hear your web developers mention these. They aren't Core Web Vitals themselves, but improving them usually improves your score.

• TTFB (time to first byte): How long the server takes to start sending data. If this is slow, everything else will be slow.
• FCP (first contentful paint): The moment the very first pixel of content (like a logo or background colour) appears. It reassures the user that the site is actually loading.

The broader page experience signals

Core Web Vitals are part of a larger family of signals. To get the full ranking boost, you need to check these boxes too:

1. HTTPS: Your site must be served over a secure connection.
2. Mobile-friendliness: The site must work flawlessly on mobile devices (no horizontal scrolling, text readable without zooming).
3. No intrusive interstitials: You cannot bombard users with massive pop-ups that cover the main content immediately upon arrival.

How to check your vitals (without a developer)

You don't need to look at code to see how you are doing. You have two primary tools to analyse performance:

1. Google Search Console (the report card):
   If you have access to your site's Search Console, look at the Core Web Vitals tab on the left. This is the most important view because it shows field data.
• Field data comes from real users (via Chrome) actually visiting your site. It accounts for real-world variables like spotty 4G connections in rural areas or older mobile devices. This is the data that affects your ranking.
2. PageSpeed Insights (the diagnostic tool):
   You can plug any URL into PageSpeed Insights.
• Look for the section labelled Discover what your real users are experiencing.
• Warning: Do not obsess over the singular Performance Score (e.g., 85/100) at the top, which is simulated lab data. Focus specifically on whether you pass or fail the three metric thresholds listed above based on the real user data.

The bottom line: speed is revenue

Core Web Vitals are often dismissed as a technical checklist, but they are actually a business asset. These days attention spans last only milliseconds, so a fast, stable site acts as your best salesperson.

To turn these metrics into a competitive advantage:

• Treat them as KPIs: Meaningful improvements happen when marketing managers and web developers share the same goals. Make LCP and INP part of your quarterly reporting.
• Prioritise mobile: Most of your users, and Google's ranking algorithm, judge you on your mobile experience. If it's slow on a phone, it's slow, period.
• Don't chase perfection at the cost of value: A green score is great. But do not remove unique product features just to achieve it. Aim for Good, not Empty.

By monitoring these vitals, you protect your search rankings and, more importantly, respect your customers' time