if you use search you will find other similar posts
use Btspeedtester but try using edge as that appears to work best - not firefox which give strange results
Speedtest.net speeds depend much on which server the info is coming from, you can select the server so make sure it is a local one. Once my speed showed very low and for some reason it was using an Australian server.
However I have just tried it and within normal tolerances I am getting the same speed reported as the BT speed test.
EDIT I am using Firefox no problems, I don't usually use Edge as I don't like it but am getting similar speeds reported using it.
Thanks for the replies.
I don't use Edge, my favourites folder kept disappearing.
Will mark this as accepted solution.