Website speed and SEO: what to measure and improve

Core Web Vitals, PageSpeed Insights, Search Console and load testing: metrics, tools and the order of fixes.

April

2021

Website speed and SEO: what to measure and improve

Website speed affects SEO through Core Web Vitals, the loading, responsiveness and visual stability metrics Google uses in ranking. Slow loading hurts conversion even more: mobile visitors leave before the first screen appears.

In short

Core Web Vitals: LCP up to 2.5 s, INP up to 200 ms, CLS up to 0.1 at the 75th percentile of visits.
Good scores alone do not secure high rankings; poor ones make it harder to beat comparable competitors.
Field data lives in Search Console and PageSpeed Insights; causes are found with Lighthouse.
Common causes: heavy images, third-party scripts, a slow server, no caching.
Start with the pages that bring enquiries and sales.

Does site speed affect Google rankings?

Site speed is judged by how content loads and how the page responds to visitor actions. Google uses Core Web Vitals in its ranking systems, yet good values alone do not secure high positions. Relevance and useful content weigh more. Speed decides when competing pages are similar in quality.

The indirect effect is bigger than the direct one. A slow page loses visitors before they see the offer and turns the same traffic into fewer enquiries.

Current Core Web Vitals

LCP: when the main large element appears; good means 2.5 seconds or less.
INP: responsiveness to interactions; good means 200 ms or less. INP replaced the older FID metric in March 2024.
CLS: visual stability; good means 0.1 or less.

Thresholds are assessed at the 75th percentile of visits, separately for mobile and desktop. A page passes only when all three metrics meet the threshold.

Which checks do you need?

PageSpeed Insights shows field data when there are enough observations, plus a Lighthouse lab analysis. Field data reflects real use; lab tests help find causes. Missing field data says nothing about site quality by itself.

The Core Web Vitals report in Google Search Console groups the site's pages by status and shows which templates underperform. To see how the server behaves under load, run k6 against an agreed test environment. A load test answers a separate question about performance at a given request rate.

Why is a website slow?

Cause	Metric affected	What to do
Large JPG/PNG images	LCP	WebP or AVIF, srcset, compression, lazy loading below the fold
Images and banners without dimensions	CLS	Set width and height, reserve space
Third-party scripts: chats, widgets, pixels	INP, LCP	Remove the unnecessary, load the rest via GTM with a delay
Slow server response (TTFB)	LCP	Page caching, a current PHP version, a CDN
Too many WordPress plugins	All	Plugin audit, caching, merging features
Fonts without font-display	LCP, CLS	font-display: swap, preload the main font

Order of improvements

Check server response, image size and loading, render-blocking resources, third-party scripts and reserved space for media. Start with pages that matter for orders: home, services, product pages, cart. After each change, measure again under comparable conditions and test forms, payment and navigation. Search Console field data covers the previous 28 days, so the effect of fixes shows up gradually, over about four weeks.

When optimisation is not enough

If the site runs on a heavy builder or an outdated theme, each fix brings only a small gain. In that case rebuilding the templates costs less: clean layout code without extra libraries and a considered redesign fix the problem at the foundation. Ongoing speed monitoring after launch is part of our website support.

Frequently asked questions

How much does speed affect SEO?

Speed is one of many signals. It rarely lifts a weak page, but it helps when competitors offer similar content and it directly affects conversion.

What PageSpeed Insights score is good?

A lab score of 90 or more is considered good, but Google cares more about field Core Web Vitals: LCP up to 2.5 s, INP up to 200 ms, CLS up to 0.1.

What is INP?

Interaction to Next Paint: the time from a visitor action (click, tap) to the next page update. INP has been part of Core Web Vitals since March 2024, replacing FID.

Where can I check my site speed?

In PageSpeed Insights for a single page, and in the Core Web Vitals report in Google Search Console for the whole site.

Will a CDN speed up my website?

A CDN such as Cloudflare delivers static files faster to visitors in different regions and reduces server load. It will not fix heavy images or scripts on its own.

Is your site slow on phones and losing enquiries?

Send us the site address. We will check Core Web Vitals in Search Console, find the causes and propose an order of fixes together with an SEO plan.

Send a requestTelegramWhatsApp

Sources

If you find an error or inaccuracy in the text, select it and press Ctrl + Enter

Comments

Write comment

Leave a request and we will contact you within 2 hours.
We will answer all your questions.