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:
iperf -c speedtest.hostkey.ru Ru(for IPv4)
iperf -c speedtest.hostkey.com NL(for IPv4)
Also you can use IPERFv3 ( -R reverse mode (server sends, client receives)
iperf3 -c speedtest.hostkey.ru RU(for IPv4)
iperf3 -c speedtest.hostkey.com NL(for IPv4)
Speedtest while downloading files from FTP or HTTP
This archive is available over Russia http Netherlands http
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)
Russian
10mb.bin 100mb.bin 1000mb.bin 2000mb.bin 5000mb.bin 10000mb.bin
Netherlands
10mb.bin 100mb.bin 1000mb.bin 2000mb.bin 5000mb.bin 10000mb.bin