Your site’s performance is quite important in an E-Commerce environment. Not only does it deter customers from coming to the site and making purchases, but Google will penalize your site as well making it so many customers won’t even find your site to come to it in the first place. So how do you measure your site’s performance?
First, you should measure the first view. That is, how long does it take for a page to load the first time a customer comes to your site. Second, you should measure the repeated view which, of course, is how long does it take for a page to load when a customer returns to the site. In order to measure this, you should look at the time to first byte (TTFB), render start, and load time.
TTFB is measured as how quickly your server will respond to a request. Render start is measured as the time it takes for the first element to appear in the browser. Load time is measured as the total time it takes to load all elements for the requested page. Once you have all this data for first and repeat views, you must measure it against typical load and peak load.
An easy way to measure page load speeds is using a free tool at webpagetest.org. It produces rather nice metrics for every element on your page. You should analyze what is happening in your page and tackle elements that are slow.
Typical things to consider are whether content is being served via a CDN, if you are using progressive JPEGs, whether your text content is gzipped, and if files could be combined to be loaded in a single request.
Good luck optimizing your site! Good results will definitely pay off.