Measure bandwidth between two computer in a LAN
Solution 1:
iPerf is designed to do exactly that and it is cross-platform. Download the version for your OS. On one of the computers run iperf -s (this is the server) and on the other run iperf -c <server hostname or IP> (this is the client). Then wait for the results. There are many options to tweak the measuring. Check iperf -hfor a complete list of options.