Core Web Vitals explained

Core Web Vitals are three measurements Google publishes to describe what using a page actually feels like. They are not a secret ranking formula and they are not a score out of a hundred. They turn three ordinary complaints into numbers instead. The page took ages to show anything. It did not respond when I tapped it. The thing I was reading jumped down the screen. Turning those complaints into numbers means two people can argue about the same problem, using the same definitions.

That shared vocabulary is the useful part for a business owner. The ranking question is smaller than the industry implies, and it is not the reason to care.

What each one measures: LCP, INP and CLS

Largest Contentful Paint answers when the main thing on the screen appeared. The browser watches the visible area while the page loads. It works out which single element is the largest piece of content in it — usually the hero image or the headline block. Then it records the moment that element finished showing. It is a stand-in for the question a visitor is actually asking: is anything useful on screen yet?

Interaction to Next Paint answers how quickly the page reacts when someone touches it. It looks at the taps, clicks and key presses across a whole visit. It measures the delay between the input and the screen visibly updating in response. Then it reports a figure for the worst of that experience, not the average. It is the measurement of a button that looks broken but is only busy.

Cumulative Layout Shift answers how much the page moved after it appeared. It accumulates every unexpected shift of visible content during the life of the page into one unitless figure. It is the measurement of the paragraph that slides away as an image loads above it.

Interaction to Next Paint replaced an earlier metric called First Input Delay. The old one measured only how long the browser took to begin handling the first interaction. That flattered pages that acknowledged a tap quickly, then did nothing visible for another second. The replacement measures through to the point where the screen actually changes — the moment a person notices.

The published thresholds for Core Web Vitals, and whose they are

Google publishes the pass marks: Largest Contentful Paint under 2.5 seconds, Interaction to Next Paint under 200 milliseconds, Cumulative Layout Shift under 0.1. Those figures are Google’s, taken from web.dev and checked on 3 August 2026. They are not a measurement made for this page and they are not this site’s opinion about what is fast.

The internal targets used on this site’s own builds are tighter — 2.0 seconds, 150 milliseconds and 0.05. The reason is plain. A site built to land exactly on the pass mark fails it the first time a tracking script, a review widget or a larger hero image is added. That usually happens within a few months of launch. Headroom is not perfectionism. It is the difference between a target that survives ordinary upkeep and one that does not.

Show the numbers behind this chart

This site's internal Core Web Vitals targets sit inside Google's published pass marks, not on them. Google publishes 2.5 seconds for Largest Contentful Paint, 200 milliseconds for Interaction to Next Paint and 0.1 for Cumulative Layout Shift as the pass marks for Core Web Vitals. This site's own internal build targets are tighter on every metric: 2.0 seconds, 150 milliseconds and 0.05 — 80 per cent, 75 per cent and 50 per cent of Google's threshold respectively.

Metric	Google's published threshold	This site's internal target	Internal target, as % of threshold
Largest Contentful Paint (LCP)	2.5s	2s	80%
Interaction to Next Paint (INP)	200ms	150ms	75%
Cumulative Layout Shift (CLS)	0.1	0.05	50%

Field data and lab data are different things in every Core Web Vitals report

This trips up nearly every conversation about site speed, so it is worth being blunt.

Lab data is a simulated load, run once, on one device profile, on one connection profile, in a data centre somewhere. It is repeatable, which makes it excellent for diagnosis: change one thing, run it again, see whether the number moved.

Field data is what real people on real devices on real connections actually experienced on your site, collected from Chrome users and aggregated over a recent period. It is what Google’s assessment is based on.

Two things follow from that. First, a lab score cannot pass or fail you, no matter how confidently a report presents it. Second, field data is grouped by a percentile of your visits, not an average. So the reported figure describes your slower visits, not your typical one. That is done on purpose. A site that works well for most people, but not for someone on a weak mobile connection outside the metro area, has a real problem — and an average would hide it.

Field data also needs enough traffic to exist at all. A low-traffic site may have no field report, which is not a pass and not a failure. It means the question has to be answered with lab tools and judgement.

What a business owner should actually do about Largest Contentful Paint and layout shift metrics

Four things, in order.

1. Look at the field data for the site you already have, in the Core Web Vitals report inside Google Search Console. That is the only place you will see what your visitors experienced rather than what a simulator predicted.
2. Separate mobile from desktop. They are reported separately because they behave completely differently, and almost every problem worth fixing is a mobile problem.
3. Treat the metrics as symptoms, not causes. No one fixes Largest Contentful Paint. They fix a hero image that was uploaded at camera resolution, or a font that blocks rendering, or a server that takes too long to answer. The metric only tells you which room the problem is in.
4. Write targets into the build agreement as acceptance criteria, measured on a mid-range phone after launch rather than on a designer’s laptop before it. Ask for the figures to be checked again a month later, when the analytics tags and the chat widget have been added.

What Core Web Vitals, PageSpeed Insights and CrUX are not

They are not a ranking guarantee, and anyone offering one is selling something they cannot deliver. They are not a design review either. They will not tell you whether the page is persuasive, whether the offer makes sense, or whether the form works. A site can pass all three and still be one that nobody can use with a keyboard. That is a separate obligation, covered under website accessibility in Australia.

Common questions about Core Web Vitals

What are Core Web Vitals? Three measurements Google publishes to describe what using a page feels like — Largest Contentful Paint (when the main content appears), Interaction to Next Paint (how quickly the page reacts when tapped), and Cumulative Layout Shift (how much the page moves after it appears). They turn three ordinary complaints — slow to show, slow to respond, jumps around — into numbers.

What are the Core Web Vitals thresholds? Google’s pass marks are Largest Contentful Paint under 2.5 seconds, Interaction to Next Paint under 200 milliseconds, and Cumulative Layout Shift under 0.1, based on field data from real Chrome users. A site built to land exactly on those marks tends to fail them once a tracking script or larger image is added, so aiming tighter leaves headroom.

Do Core Web Vitals affect Google rankings? They are a ranking input, but a small one, and it is not the main reason to care. They are not a ranking guarantee. The useful part is a shared vocabulary for what a page feels like to use, so problems can be defined and fixed.

Where to go from here

If the terminology here is still slippery, the plain definitions of these and the other words that turn up in a web quote are collected in the glossary. For where speed is actually decided — platform, hosting, build pipeline, third-party scripts — the underlying engineering is set out on development work in Brisbane.