How heavy should a web page be, and why is my site slow?
Around 2 MB or less is a sensible weight for a page. Under a second before the page starts arriving is good. Most slow sites fail on one of four things: the server takes too long to answer, the page is too heavy, too many files hold up the first view, or nothing is compressed or cached.
How the check knows
It fetches your page once, times how long the server takes to start answering, then asks each file the page uses how big it is without downloading it. It looks at whether the server shrinks pages before sending them, whether browsers are allowed to keep a copy of your files, and which scripts sit in the head of the page where they block everything behind them.
What each finding means
The server is slow to answer. This is the wait before anything happens, and it’s usually hosting or an unoptimised WordPress doing too much work on every visit. More than two and a half seconds is a real problem.
The page is heavy. Almost always images: photos uploaded straight from a phone at full size. Over 5 MB and people on mobile will leave.
Scripts hold up the first view. Code loaded before the page can draw. Plugins and page builders are the usual source, and every one of them loads on every page whether it’s used there or not.
Pages aren’t compressed. Text can be shrunk to a fraction of its size on the way to the browser. Most hosts turn this on; some don’t.
Files aren’t cached. Returning visitors download everything again because the server never told their browser it could keep a copy, or only let it keep one for a few hours. The check, like Google’s, wants at least a day.
What you can do yourself
Resize photos before you upload them; 1,600 pixels wide is plenty for most pages. Delete plugins you don’t use. If your host offers a caching option or a content delivery network in its control panel, turn it on. Those three fix the majority of slow sites.
When it’s a developer’s job
Slow server responses on a site that’s already been tidied, scripts you can’t remove because a page builder or a theme needs them, or a site that has had every plugin thrown at it and is still slow. Matt measures first and tells you what’s realistic, and he’ll say plainly if the honest answer is that the builder has to go.