How fast should a site be? Core Web Vitals in plain words
· 3 min read · CLICKO
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Three Google metrics that show whether a site loads fast, responds instantly and does not "jump around". What they mean and how to improve them.
A "fast site" is not a feeling, it is measured. Google uses three metrics, the Core Web Vitals, and takes them from real visitors, not from a lab test.
Why every tenth of a second counts, according to a Deloitte study of 37 brands:
8.4%
more conversions for retail sites when their mobile site got 0.1 seconds faster.
Source: Deloitte, Milliseconds Make Millions (web.dev), June 2020
10.1%
more conversions for travel sites with the same improvement.
Source: Deloitte, Milliseconds Make Millions (web.dev), June 2020
9.2%
more money spent by retail customers.
Source: Deloitte, Milliseconds Make Millions (web.dev), June 2020
The three metrics
- LCP (Largest Contentful Paint): how long it takes for the largest element on the screen to appear, usually the main image or the heading.
- INP (Interaction to Next Paint): how quickly the page reacts when you tap something. It replaced the older FID in March 2024.
- CLS (Cumulative Layout Shift): how much elements move around while the page loads. It is the annoying "I went to tap the button and it moved".
The thresholds
| Metric | Good | Needs improvement | Poor |
|---|---|---|---|
| LCP | up to 2.5 s | 2.5 to 4 s | over 4 s |
| INP | up to 200 ms | 200 to 500 ms | over 500 ms |
| CLS | up to 0.1 | 0.1 to 0.25 | over 0.25 |
A page passes when at least three out of four of its visitors have a good experience on each metric.
LCP is the one that fails the most sites:
Source: HTTP Archive, Web Almanac 2025, July 2025
Enter your site's values from PageSpeed Insights and see how Google rates them:
Put in your own numbers
Check your Core Web Vitals
2.2 sGood
180 msGood
0.05Good
You pass all three of Google's thresholds.
Source: Google, web.dev, October 2026
Where to see them
In Google's PageSpeed Insights you enter your site's address and see the metrics from real users, if there are enough visits. In Search Console, the Core Web Vitals report shows which pages have a problem.
The 5 most common problems on Greek e-shops
- A slider with heavy photos on the first screen. LCP waits for an image of several MB, often behind the script that builds the slider. A single static image in WebP, at the right size, makes the biggest difference.
- Cheap hosting without caching. Especially on WooCommerce, the server is slow to respond before the page even starts loading, and that hurts LCP on every page at once.
- Lots of third party scripts. Pixels for Meta, Google and TikTok, chat, reviews, popups. Each one looks small; together they keep the phone busy and hurt INP.
- Bars and banners that push the page down. A free shipping bar, an offer or a cookie banner that appears after the content has loaded and pushes it down. The most classic cause of poor CLS.
- Themes and apps that load everything everywhere. A theme with dozens of features loads code for all of them on every page. On Shopify, uninstalled apps often leave code in the theme that keeps loading.
What helps most
- Images at the right size and in a modern format such as WebP, not a 4000 pixel photo inside a 400 pixel box.
- A declared width and height on images and videos, so their space is reserved before they load.
- Fonts served from the site itself, with the text visible until they load.
- Fewer third party scripts. Every chat, pixel and widget adds work for the visitor's phone.
- Anything not visible on the first screen loads later.
What not to expect
A score of 100 out of 100 in a lab test is not the goal. The goal is for your real visitors, on their own phones and their own connections, to quickly see what they came for. Speed is one of many ranking factors. It will not lift a page with weak content on its own, but a slow page loses visitors before they even read.
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