In brief: to improve your website's loading speed, measure it first with Google PageSpeed Insights, then fix the biggest slowdowns: oversized images, too many scripts, missing caching and slow hosting. Google rates user experience with the Core Web Vitals. Good values are a load time for the largest content element (LCP) of up to 2.5 seconds, a response time (INP) of up to 200 milliseconds and a layout shift (CLS) of up to 0.1.
Why does loading speed matter?
A slow page costs you visitors. Someone staring at a blank page on their phone will quickly tap back and pick the next search result. You lose that visit, and often the enquiry or purchase that would have followed.
User experience also plays a part for Google. The Core Web Vitals are among the signals Google uses to assess page experience. Good content still carries more weight: a fast page without a fitting answer will not rank on speed alone.
What are the Core Web Vitals?
Google measures user experience with three metrics. The thresholds apply to real visitors and refer to the 75th percentile, meaning three out of four page views:
| Metric | What it measures | Good | Needs improvement | Poor |
|---|---|---|---|---|
| LCP (Largest Contentful Paint) | When the largest visible content has loaded | up to 2.5 s | up to 4.0 s | over 4.0 s |
| INP (Interaction to Next Paint) | How quickly the page responds to clicks and input | up to 200 ms | up to 500 ms | over 500 ms |
| CLS (Cumulative Layout Shift) | How much content shifts while loading | up to 0.1 | up to 0.25 | over 0.25 |
INP replaced the older FID metric in 2024. That is why older guides sometimes still mention FID.
How do I measure loading speed?
- PageSpeed Insights: Google's free tool shows two kinds of data. Field data comes from real Chrome users, provided there are enough visits. Lab data is produced by a simulated test. Below that, the tool lists specific improvements.
- Google Search Console: the Core Web Vitals report shows which groups of pages perform well, need improvement or perform poorly.
- Lighthouse: built into the Chrome browser (developer tools), it provides lab data similar to PageSpeed Insights.
Always measure the mobile view first. Values there are usually worse, and many visitors arrive on their phones.
How do I optimise images?
On many websites, images are the biggest slowdown. These steps often bring the largest gain:
- Right size: do not upload images larger than they are displayed. A photo straight from the camera is almost always far too big for a website.
- Modern formats: at the same quality, WebP and AVIF are usually smaller than JPEG or PNG.
- Compression: tools for shrinking images save file size without any visible difference.
- Lazy loading: images further down the page only load once the visitor scrolls there.
- Fixed dimensions: specify width and height. The browser then reserves the space and nothing shifts, which improves the CLS value.
One exception to lazy loading: the large image right at the top should load immediately, because it is often exactly the element that determines the LCP value.
How do I reduce scripts and CSS?
Every script has to be loaded, parsed and executed. Many websites load code that is no longer needed at all: old tracking snippets, unused plugins, chat widgets or animations.
- Remove anything you do not really use.
- Delay scripts that are not needed straight away (the "defer" or "async" attributes).
- Combine files and strip out spaces and comments (minification).
- Check your fonts: every extra typeface and every extra font weight adds loading time.
What do caching and a CDN do?
Browser caching means that a returning visitor does not have to download files such as the logo, fonts and stylesheets again. The server tells the browser how long it may keep these files.
A content delivery network (CDN) spreads copies of your files across servers in many locations. Visitors receive the data from the server closest to them. This shortens the distance the data travels, especially for visitors from other countries.
What role does hosting play?
If the server takes a long time to respond at all, every other measure can only help so much. This waiting time is called Time to First Byte (TTFB). If it stays high, it is worth looking at your hosting plan, the server location or switching provider. With website builders and content management systems, the number of plugins can also slow the server down.
How do I stop content from shifting?
You probably know this: you are about to tap a link, and suddenly the text jumps down because an image or banner has loaded above it. That is exactly what CLS measures. The fixes are fixed dimensions for images and videos, reserved space for banners and ads, and fonts that do not change the line length while loading.
In what order should I proceed?
- Measure the mobile home page and your most important subpages with PageSpeed Insights.
- Shrink images, convert them to WebP and switch on lazy loading.
- Remove unused plugins, scripts and fonts.
- Turn on caching and, if possible, use a CDN.
- Measure again and compare with the first result.
- Only then think about hosting or larger rebuilds.
Common mistakes
- Testing only on the fast desktop computer in the office
- Treating the PageSpeed Insights score as more important than real field data
- Installing new plugins to speed things up while the old ones stay in place
- Lazy loading the large image at the very top
You can read more about building and designing fast websites on our Web Design topic page.
Sources: Google (Core Web Vitals thresholds, PageSpeed Insights, Google Search Console Core Web Vitals report), Lighthouse in Chrome DevTools.