Knowing the speed of your Internet connection can be handy to distinguish whether a slow-moving download is caused by a problem with your computer or a problem with your Internet connection, to see if your Internet Service Provider (ISP) is delivering the bandwidth it promised, and to judge how long it will take to download files.
There are two methods to check your Internet speed: ISP software already on your computer, and online speed-testing websites.
Your Internet service may have come with proprietary software to be installed, especially if you have a high-speed connection such as DSL or cable; dial-up connections and Internet service through cell-phone tethering or a USB modem may come with special software such as Verizon's VZAccess or Alltel's Access to connect you to the web.
Open your software and look for a tab marked 'Statistics' while you are connected to the Internet. In that tab will be a graph showing your transmit rate (or "upload") and receive rate (or "download").
There are many websites to test your bandwidth if you don't have ISP software; a few of the better known sites are AuditMyPC, which offers several other tools besides a speed check; Bandwidth Place, which offers a simple, interactive test; and SpeedTest, which allows you not only to test the speed of your connection, but also compare it against other speeds and features a 'Test Again' button if you wish to test several times and average those numbers for a baseline speed. SpeedTest also lets you choose your test location from a selection of sites across the country, although you'll get the best numbers if you test a site close to your physical location.
What the Numbers Mean
There are three critical numbers for determining your Internet speed: ping, download bandwidth, and upload bandwidth.
Ping is a measure of speed; it calculates the time it takes for a small file to be sent from your computer to an Internet server and back again. It is like a submarine using sonar to determine the distance an object is from the boat, sending out a sound wave and counting how much time it takes for the sound to bounce off the object and return as an echo. With an online ping, the smaller the number, the better, as that represents a fast Internet connection.
Upload and download bandwidth isn't a measure of speed; it measures how much information can be transferred up or down at one time. If you look at your data transfer as an information highway, then the download bandwidth represents how many lanes there are leading into your computer; more lanes mean faster downloads. The upload bandwidth represents how many lanes are leading out of your computer to the Internet, and the ping is the speed limit of the data traveling those lanes.
Those numbers can help you determine how long a file download will take; SpeedTest even gives you a chart showing the time needed for various files.