A slow website costs you twice. Visitors leave before it finishes loading, and Google takes speed into account when it decides how to rank your pages. "It feels slow" is hard to act on, though. Three numbers tell you why a site is slow, and each one points to a different fix.
You can see all three for your own site in a couple of minutes. Go to PageSpeed Insights at pagespeed.web.dev, Google's free checking tool, and enter your address. It shows the mobile results first. Most of your visitors are probably on phones, so those are the ones to read.
1. Load time
The first number is how long it takes for the main thing on the page to appear. Google measures this as LCP, short for largest contentful paint: the moment the biggest image or block of text on the screen has finished showing.
Google's guidance is that this should be 2.5 seconds or less.
It is like waiting for a meal in a restaurant. The bread arriving quickly is nice, but what you notice is how long the main course takes. LCP measures the main course.
Common causes. A large image at the top of the page, often a photo uploaded straight from a camera. Fonts or scripts that must load before anything can show. A slow server, which is the third number below.
What to do. Resize the main image to the size it is shown at, and save it in a modern format such as WebP or AVIF, which keep the same quality at a fraction of the file size. Then check the third number, because a slow server delays everything.
2. Page weight
The second number is the total size of everything the page downloads: its images, fonts, scripts, and styles, measured in megabytes. PageSpeed Insights lists the largest files under its diagnostics.
Every megabyte has to travel to the visitor's phone, often over a mobile signal. A single photo taken on a modern phone can be several megabytes on its own, so a page with a few unprepared photos quickly becomes heavy.
Common causes. Images uploaded at full size. Scripts added over the years for chat windows, tracking, and plugins, some of them no longer used. Several font files where one or two would do.
What to do. Resize and convert images, as above. Use lazy loading, which waits to download an image until the visitor scrolls near it. Then go through the scripts on the site and remove any that nobody can explain.
3. Server response
The third number is how long your server takes to start sending the page at all. This is called TTFB, short for time to first byte. Nothing can appear until it is over.
Google's guidance is that it should be 0.8 seconds or less. Over 1.8 seconds is counted as poor.
Common causes. Low-cost shared hosting, where your site shares a server with many others. A server a long way from your visitors, such as a UK business hosted in the United States. Pages rebuilt from scratch for every visitor instead of being saved and reused.
What to do. Turn on caching, which keeps a ready-made copy of each page so the server does not rebuild it every time. Use a CDN, short for content delivery network: copies of your site held on servers around the world, so each visitor is served from one nearby. If neither helps, the hosting itself is the problem, and moving is often the single biggest improvement you can make.
Which to fix first
Start with whichever of the three is furthest from its target. If server response is slow, fix that first, because it delays everything else. If it is fast but load time is not, the page itself is too heavy, and images are almost always the place to start.
Check again after each change. Speed improvements are easy to measure, which makes them some of the most satisfying fixes on a website.
We build fast websites and speed up existing ones. If yours fails these checks, get in touch.
Glossary
- LCP (largest contentful paint): how long until the biggest image or block of text on the screen has appeared.
- Page weight: the total size of everything a page downloads, in megabytes.
- TTFB (time to first byte): how long the server takes to start sending a page.
- WebP and AVIF: modern image formats that keep the same quality in much smaller files.
- Lazy loading: downloading an image only when the visitor scrolls near it.
- Caching: keeping a ready-made copy of a page, so it does not have to be rebuilt for every visitor.
- CDN (content delivery network): copies of your site on servers around the world, so each visitor is served from one nearby.
- Hosting: the server your website lives on.