Alternatively you can use
gkrellm to monitor your connection speed in real time. As you can guess, in order to get a useful measurement you'd need to download a relatively large file, such as starting an ISO download (obviously you'd want to cancel it after 15 or 20 seconds, but that's enough to see what kind of speed you're getting)
As an aside, there are many factors that can affect speed, such as the level of traffic on the site you're trying to visit, as well as the level of traffic on your network (assuming you're on one)