I needed to check the download speed on of an interface on my Raspberry Pi, so I have used a tool called speedometer to do so.
The tool can be installed like this on Raspbian Lite.
sudo apt-get install speedometer
What I needed to see is a view without a graph, just the raw data (-p) refreshed every 1 second intervals (-i 1) and just the download a.k.a received on the eth0 interface (-r eth0).
speedometer -p -r eth0 -i 1