Performance Metrics

A lot of emphasis is placed on the performance of a website these days. According to an Akamai study, a 100ms increase in website load time decreases conversion rates by 7%. But how do you measure performance? Do you consider only the time spent on the server to create the response page? Do you include the network delay, too?

These days, two types of metrics are popular: time to first byte and page load time.

• Time to first byte, as shown in the illustration below, is the time from the issuance of the HTTP request until the web browser receives the first byte of the response. The reason this metric is important is that the browser can start parsing the response as soon as it starts receiving the response.

• Page load time, on the other hand, is the time since the issuance of the HTTP request until the page has finished loading completely.