Iperf software and manuals can be found on its official home page https://iperf.fr
You can find a TCP Throughput calculator here.
For a more accurate test, use commands like:
Also you can use IPERFv3 ( -R reverse mode (server sends, client receives)
For a more accurate test, use the command like:
wget -4 -O /dev/null "https://speedtest.hostkey.ru/ftp/2000mb.bin" RU(for IPv4)
wget -4 -O /dev/null "http://speedtest.hostkey.com/2000mb.bin" NL(for IPv4)