Page Speed & PerformanceComplete Guide14 min readPublished 24 February 2026
Website Speed and Sales: The Complete Guide to How Fast Your Site Needs to Be
Alexander Rule
Founder, Northrule SEO
Page speed is the time it takes for your web page to fully load and become usable in a visitor's browser. It is not a single measurement — it is a collection of metrics that together determine whether your site feels fast or frustratingly slow. For businesses, page speed is a revenue metric: every second of delay costs you customers, rankings, and money.
Most business owners know their site "could be faster" but have no idea what "fast enough" actually means, which metrics matter, or where to start fixing things. This guide covers all of it — from the specific measurements Google uses to rank your site, to the practical fixes that deliver the biggest commercial return.
This is not theoretical. The relationship between page speed and revenue is one of the most researched topics in digital marketing.
Google's own research found that as page load time increases from 1 to 3 seconds, bounce probability increases by 32%. From 1 to 5 seconds, it increases by 90%. That means nearly all of your additional visitors leave before seeing your content if your site takes 5 seconds to load.
Research from Portent confirmed that a site loading in 1 second achieves a conversion rate 3x higher than a site loading in 5 seconds. Each additional second of load time reduces conversions by approximately 4.4%.
For a business generating £10,000 per month online, shaving 2 seconds off load time could recover £500–£1,000 in monthly revenue — without changing a single word of copy or spending a penny more on advertising.
Speed is also a confirmed Google ranking factor. Since 2021, Core Web Vitals — a set of speed and user experience metrics — directly influence where your pages appear in search results. Faster pages rank higher, which means more traffic, which means more revenue.
Your website platform and tech stack set the baseline for how fast your site can be. But even the best platform produces a slow site if the content is bloated, the hosting is poor, or the code is unoptimised.
There are dozens of ways to measure website speed. These are the six that matter commercially:
| Metric | What It Measures | Good | Needs Work | Poor |
|---|---|---|---|---|
| TTFB | Time to First Byte — server response speed | < 200ms | 200–600ms | > 600ms |
| FCP | First Contentful Paint — when anything first appears | < 1.8s | 1.8–3.0s | > 3.0s |
| LCP | Largest Contentful Paint — when main content loads | < 2.5s | 2.5–4.0s | > 4.0s |
| CLS | Cumulative Layout Shift — visual stability | < 0.1 | 0.1–0.25 | > 0.25 |
| Total Page Size | All files downloaded to display the page | < 1MB | 1–3MB | > 3MB |
| Fully Loaded Time | Everything finished loading | < 3s | 3–6s | > 6s |
The first four are what Google measures. The last two are what your visitors feel. Together, they give you a complete picture of your site's speed performance.
TTFB measures the time between a visitor clicking a link to your site and their browser receiving the very first piece of data from your server. It is the starting gun — everything else waits for it.
A slow TTFB means your server is taking too long to respond. This is usually caused by poor hosting, server location being far from your visitors, lack of caching, or slow database queries. No amount of front-end optimisation fixes a slow server.
The target is under 200 milliseconds. Anything over 600ms is a problem that needs immediate attention.
Our detailed guide on what TTFB is and why it affects your rankings covers the causes, how to test it, and the fastest fixes. TTFB is also the central concern of server response time optimisation, which covers the infrastructure decisions that determine your baseline speed.
FCP measures the moment something — anything — first appears on screen. It could be text, an image, or your navigation bar. Before FCP, your visitor is staring at a blank white screen.
Users form an opinion about your website within 50 milliseconds. If that first impression is a blank screen that hangs for 2–3 seconds, the opinion is negative before your content even loads. Many visitors will not wait to find out what comes next.
The target is under 1.8 seconds. The most common causes of slow FCP are render-blocking CSS and JavaScript, slow web font loading, and a poor TTFB dragging everything else down.
Our guide to First Contentful Paint explained covers what affects it and how to fix the most common issues.
LCP is the speed metric Google cares about most. It measures when the largest visible element on your page finishes loading — typically your hero image, main heading, or a large block of text.
LCP is a confirmed Core Web Vital and a direct ranking signal. It is also the metric that fails most often. Google's own data shows that the majority of websites fail the LCP threshold on mobile.
The target is under 2.5 seconds. Over 4 seconds is classified as poor. The most common causes of poor LCP are unoptimised hero images, slow server response, render-blocking resources, and excessive page weight.
Our detailed guide on Largest Contentful Paint optimisation includes a quick-wins checklist that addresses the most common failures. LCP sits within the broader framework of Core Web Vitals, which Google uses as part of its page experience ranking signals.
CLS measures how much your page layout moves around while it loads. It captures those frustrating moments where you are about to tap a button and an ad loads above it, pushing everything down. Or a font loads and all the text reflows. Or an image slot expands and shoves the content you were reading off screen.
CLS causes accidental clicks, frustrated users, and abandoned sessions. On mobile, where screen space is limited and tap targets are smaller, even small layout shifts cause problems.
The target is under 0.1. Over 0.25 is poor. The most common causes are images and videos without explicit dimensions, dynamically injected content (ads, pop-ups, cookie banners), and web fonts that cause text reflow.
Our guide on fixing Cumulative Layout Shift covers the specific fixes for each cause. CLS is another Core Web Vital that directly affects your Google rankings.
Not all pages on your website face the same speed challenges or carry the same commercial stakes.
Your homepage is your first impression — a slow homepage means visitors bounce before seeing what you offer. Your product pages carry direct conversion weight — a slow product page kills sales. Category and listing pages are browsing pages — if they are slow, visitors never reach your products. And your checkout page is the final step — a slow checkout page means abandoned carts and lost revenue.
Each page type has different speed targets, different common problems, and different fixes. Product listing pages with heavy filtering and sorting consistently score worst on speed tests because they load large amounts of dynamic content.
Our guide on page speed by page type gives you specific benchmarks and priorities for every page on your site. How your pages are organised also affects performance — site structure determines how many resources each page needs to load.
Total page size is exactly what it sounds like — the combined weight of every file a browser needs to download to display your page. This includes HTML, CSS, JavaScript, images, fonts, and third-party scripts.
The average web page in 2025 is approximately 2.5MB. On a decent broadband connection, that loads in a couple of seconds. On a mobile 3G connection — which is still common in rural areas and during travel — 2.5MB takes 10 seconds or more.
Images account for 50–70% of most pages' total size. They are almost always the single biggest opportunity for improvement. But third-party scripts — analytics, chat widgets, marketing pixels, A/B testing tools — add up silently and are often overlooked.
Our guide on reducing website page size covers image compression, code minification, lazy loading, and how to audit the third-party scripts that are quietly bloating your pages.
Google PageSpeed Insights is the standard tool for measuring website speed. It is free, it uses real user data, and it tells you exactly what to fix. But the report is designed for developers, not business owners, and it is easy to misread.
The performance score (0–100) gets the most attention, but it is the Core Web Vitals assessment that actually affects your rankings. A site can score 60 on the performance scale but still pass all Core Web Vitals — and vice versa. Knowing which numbers matter and which are noise is the difference between effective optimisation and wasted effort.
Our guide on how to read a PageSpeed Insights report walks through every section of the report in plain language, tells you what to worry about and what to ignore, and gives you a clear action list to send to your developer.
Understanding PageSpeed Insights is also your entry point into Core Web Vitals — the specific metrics Google uses to evaluate your site's user experience.
You do not need to understand every metric to start improving your site speed. Here are the five things to do today:
Run a PageSpeed Insights test — Go to pagespeed.web.dev, enter your homepage URL, and look at the Core Web Vitals section. If any metric is red, you have a problem worth fixing.
Test mobile, not just desktop — Google uses your mobile score for rankings. Desktop speed is almost always better than mobile, so testing only on desktop gives you a false sense of security. PageSpeed Insights defaults to mobile — keep it there.
Check your largest images — Right-click your homepage, select "Inspect," go to the Network tab, and sort by file size. If any single image is over 200KB, it needs compressing. If you see images over 1MB, that is likely your biggest speed problem.
Count your third-party scripts — In the same Network tab, filter by "JS" and look at how many scripts load from external domains (anything not your own website). Each one adds load time. If you count more than 10, you have script bloat.
Test from a mobile device — Load your site on your phone using mobile data (not WiFi). Time it. If you are waiting more than 3 seconds to see content, your mobile visitors are too.
Page speed is not a vanity metric. It directly affects where you rank in Google, how many visitors stay on your site, and how many of them convert into customers. The relationship is clear, the data is conclusive, and the fixes are achievable.
The guides in this series cover each speed metric in the depth it deserves. Start with the one that is most relevant to your situation — or work through them all for a complete understanding of how speed affects your business.
If you want a professional assessment of your site's speed performance, including specific recommendations prioritised by commercial impact, talk to us about an SEO audit. We test every metric covered in this guide and tell you exactly where you are losing money — and what to fix first.
For a straightforward conversation about your site's speed, get in touch.
A good page speed means your Largest Contentful Paint (LCP) loads in under 2.5 seconds, your First Contentful Paint (FCP) appears in under 1.8 seconds, and your Time to First Byte (TTFB) is under 200 milliseconds. These are Google's own thresholds. For commercial impact, research shows that pages loading in 1 second convert at 3x the rate of pages loading in 5 seconds.
Yes. Google has confirmed that page speed is a ranking factor, particularly through Core Web Vitals — Largest Contentful Paint, Cumulative Layout Shift, and Interaction to Next Paint. Slow sites rank lower, receive less organic traffic, and lose visibility to faster competitors in the same search results.
Use Google PageSpeed Insights (pagespeed.web.dev) for a free, detailed report. It measures your Core Web Vitals, gives a performance score out of 100, and lists specific opportunities to improve. Test both your mobile and desktop versions — mobile is what Google uses for ranking.
Largest Contentful Paint (LCP) is the most commercially important speed metric. It measures when the biggest visible element on your page finishes loading — usually your hero image or main heading. Google uses it as a Core Web Vital ranking signal. If you can only fix one metric, fix LCP.
Yes. Google uses mobile-first indexing, meaning it ranks your site based on the mobile version. Mobile connections are also slower and less reliable than desktop broadband, so speed issues are amplified. Over 60% of web traffic is mobile, so a slow mobile experience affects the majority of your visitors.
Google research shows that as page load time increases from 1 to 3 seconds, bounce probability increases by 32%. From 1 to 5 seconds, it increases by 90%. Portent found that each additional second of load time reduces conversions by roughly 4.4%. For a site generating £100,000 per year, a 2-second improvement in load time could recover thousands in lost revenue.
The most common causes are unoptimised images (often 50–70% of total page size), slow hosting or server response, render-blocking CSS and JavaScript, excessive third-party scripts (analytics, chat widgets, marketing pixels), uncompressed files, and too many HTTP requests. Most slow sites have multiple issues compounding each other.
Some fixes are straightforward — compressing images, removing unused plugins, and switching to a faster DNS provider can all be done without code changes. However, issues like render-blocking resources, JavaScript optimisation, and server configuration typically require developer support. A Google PageSpeed Insights report will tell you what needs fixing and how complex each fix is.
Cumulative Layout Shift measures how much your page layout moves while loading. Shifting buttons, expanding images, and reflowing text cause accidental clicks, frustration, and lost sales. This guide covers the fixes.
6 min readFirst Contentful Paint is the moment anything first appears on your visitor's screen. Users form an opinion in 50 milliseconds. This guide explains what affects FCP, the thresholds that matter, and how to fix it.
5 min readGoogle PageSpeed Insights gives you a detailed speed report for any web page. But the report is designed for developers. This guide explains every section in plain English and tells you what matters, what to ignore, and what to send your developer.
6 min readLargest Contentful Paint measures when your main content finishes loading. It is a confirmed Google ranking signal and the metric that fails most often. This guide covers thresholds, causes, and quick wins.
6 min readYour homepage, product pages, category pages, and checkout all face different speed challenges. This guide gives you specific benchmarks for each page type and tells you which to prioritise.
7 min readThe average web page is 2.5MB. On a mobile 3G connection, that takes 10+ seconds to load. Images account for 50-70% of the total. This guide covers how to reduce page size and stop losing mobile customers.
6 min readTTFB measures how quickly your server responds when someone visits your site. A slow TTFB delays everything else. This guide explains what affects it, the thresholds that matter, and how to improve it.
5 min readSubscribe to get our latest guides, tutorials, and success stories delivered to your inbox
Cumulative Layout Shift measures how much your page layout moves while loading. Shifting buttons, expanding images, and reflowing text cause accidental clicks, frustration, and lost sales. This guide covers the fixes.
Read More →First Contentful Paint is the moment anything first appears on your visitor's screen. Users form an opinion in 50 milliseconds. This guide explains what affects FCP, the thresholds that matter, and how to fix it.
Read More →Google PageSpeed Insights gives you a detailed speed report for any web page. But the report is designed for developers. This guide explains every section in plain English and tells you what matters, what to ignore, and what to send your developer.
Read More →