Speed testing is easy to misread, and people frequently optimise the wrong thing as a result.
THE TOOLS
GTmetrix gives a waterfall chart showing exactly what loaded, in what order, and how long each item took. This is the most useful view. Google PageSpeed Insights reports Core Web Vitals, which is what Google actually measures for ranking. WebPageTest allows you to choose a test location, which matters if your audience is not where you are.
READING THE RESULTS
Look at the first response time, sometimes shown as Time to First Byte. If that is slow, the problem is server-side: caching, PHP, plugins or database. Look at total page weight. If that is large, the problem is assets: images, scripts and fonts. Ignore the overall letter grade in isolation. A site can score well and still feel slow to a real visitor.
TESTING FAIRLY
Test the same page three times and use the later results, since the first run populates caches. Test from a location near your actual audience. Test in a private browsing window, and while logged out, as logged-in views bypass caching. Change one thing at a time and re-test, or you will not know what helped.
