Why Is My Ethernet So Slow but Wi-Fi Is Decent?

I'm subscribed to a 1 Gbps ISP and have a 30ft Cat6 cable running from my router to my computer, but I'm only getting about 10 Mbps according to the Google speed test.

When I switch to Wi-Fi from the same router, my phone and tablet show speeds between 70-80 Mbps using the same speed test.

However, when I unplug the Ethernet cable from my PC and switch to Wi-Fi, my PC still only gets around 10 Mbps. All these tests were done using a Los Angeles server. Any idea what's causing this?
 
Have you tried swapping out the Ethernet cable just to rule out a faulty cable? Also, make sure your PC's network adapter drivers are up to date. Sometimes it's just a little thing like that causing all the hassle.
 
Weird issue! Maybe check your router settings too. Sometimes specific devices can get limited if the QoS settings are weird. Also, try plugging your PC into a different port on the router. I've had ports go bad on me before, and it messed with my speeds.