How to check your Ethernet cable’s speed

A wired Ethernet connection does not guarantee fast internet, and a speed test cannot tell whether the cable is the cause of a slow result. Checking the negotiated link speed can help identify where to investigate, but it measures the connection between a computer and its router or switch, not internet speed or the cable’s maximum capacity.

Windows and Mac settings show the link speed, which should be left on Automatic. Cat5e and Cat6 can both support gigabit Ethernet; if the reading is only 100 Mbps, check that both ports support gigabit, reseat the connectors and try a known-good cable. To compare actual local network throughput without involving an internet provider, the article suggests using iPerf3 between two wired computers.