The following two debian tools makes it very easy to accurately measure your internet connection speed as well as in your LAN.
Measuring internet connection speed
sudo apt install speedtest-cli
Run it by typing:
speedtest-cli
Measuring LAN connection speed
sudo apt install iperf3
Run the server in one device which will be listening for the client to establish a connection.
iperf3 -s
In your other network device install iperf3 and run the client against the server:
iperf3 -c [server's ip address]
Results should show up promptly