If you are using an internet "speed test" site, make sure you find and try half a dozen or so.
There seems to be massive variation in the results, possibly due to differences in methods, algorithms and inferences - not to speak of congestion at THEIR end if they are timing the upload of files to your PC! Add to this the possibility of caching along the route...
For example, 3 sites report my (cable) connection speed at about 800 kbps, whereas another 3 report it as around 3800kbps.
Yet another couple of sites put it at about 1200 Kbps.
It is nominally 4Mbps, btw
Given the grouping around these numbers I suspect the methods used are different - but I have no real idea of how the testing is done (apart from timing the download of files).
SD