While measuring the response time is not so difficult, reading into it and finding the exact cause of the slowdown is not that easy a task. So, to be able to precisely pinpoint why your site is loading slowеr than you’d expect, first you need to know the components of the response time.
On the whole, response time comprises four parts: DNS lookup time, Connection time, Redirect time, First byte and Last byte.
The DNS Lookup time is the time that is needed to resolve the website’s hostname to a certain IP address. Usually, if the DNS lookup time is high, it means that you might have a problem with your DNS servers. Keep in mind that most providers cache the DNS record for a specific time indicated at the so called "DNS zone" file, so when monitoring your site, the DNS lookup time affects the response time only once in case of multiple references pointing to the same domain name.
The second part - the Connection time - shows how long it takes to establish a connection to your server. This measurement can help you monitor your network latency. It is also a good indicator for routing or network issues.
Redirect time is the time it takes to follow any HTTP redirects in the server’s response. It also comprises the time for any DNS lookups or connection times that might occur during this process.
The First byte shows how long it takes from the moment the connection was created until the first byte is about to be transferred. The time to perform any negotiations with the server and the time needed for the server to calculate the result are also included. The First Byte time is measured in seconds, and, when too high, may indicate a problem with the server load.
The time necessary to download the final server response is called Last byte. Generally, you can use this value as a good bandwidth indicator - if it is too high you may want to decrease the page size or upgrade your bandwidth in order to increase the download speed from your site or server.
So, now that you know how to read the response time, why don’t you test the response time of your site here?