How can we consider the load speed of a website?

We know if the content is heavy in website then it will take a much time than website having content in lower.

Suppose, if we have 1mb page size then the site will load slower than the page size having 1kb.

But I am trying to understand how can we consider the loading speed if the page size is just 1kb and url is hit by millions of user simultaneously.

Hitting url by one user will be faster enough. But hitting the same url simultaneously by millions of user will be time consuming?

Here I would like to know if the speed depends on page size or it also depends the url hit by simultaneous users.