I have a gigabit internet plan, but my Windows 11 PC only reaches around 90 Mbps over Ethernet. Windows reports the Ethernet connection as 1000/1000 Mbps, and my phone gets roughly 700 Mbps when tested near the main router on the floor above. The PC is connected through several Cat6 cables, two female-to-female couplers, and a secondary Mercury router. My drivers are up to date, Wi-Fi is disabled, and setting Speed & Duplex to Auto or 2.5 Gbps did not improve the result. What should I check or replace?
3 Answers
A speed test around 90 Mbps usually means that one part of the wired path has negotiated at 100 Mbps, even if the PC’s adapter page displays 1000/1000. Check the Ethernet status on every device involved, especially the secondary router, its WAN/LAN ports, and any switches or adapters. Test the PC directly against the main router with one known-good cable if possible.
Your secondary Mercury router may also be limiting the connection. Confirm that its ports are gigabit-capable and that the cable is connected to the correct LAN/WAN port. If it is acting as an older repeater, switch, or access point, bypass it temporarily and compare the speed with a direct connection. Wi-Fi being off on the PC is good, but it does not rule out a slow wired device somewhere upstream.
The likely weak points are the couplers, wall terminations, connectors, or one damaged cable. Gigabit Ethernet needs all four twisted pairs; if a pair is broken or terminated badly, the link can fall back to 100 Mbps. Replace each cable and coupler one at a time, or use a cable tester to find the faulty section.
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