I have three computers in my home. My old computer is a lenovo w530 running windows 10 and my new computers are a 13'' and 15'' inch macbook pro 2015.

All computers are connected to the same wifi router.

if I connect my windows machine and my 13'' macbook pro to www.speedtest.net it report a internet connection speed of Download: 57.65 Mbps Upload: 57.96 Mbps

when I do the same thing on my 15'' macbook i see connection speed of Download: 3.2 Mbps Upload: 0.59 Mbps

Why is 15'' mac so slow for wifi as compared to my 3 year old windows and 13'' inch macbook pro?

Edit:: Here are the details requested below

RSSI: -37dBm
Noise: -93dBm
TxRate: 117 Mbps
MCS Index: 15
CountryCode: US
  • Can you hold Option down, click on the WiFi icon on the top right, and tell us what it reports as your RSSI, Noise, Tx Rate, PHY Mode and MCS Index? It would give us a little more info. – William T Froggard Nov 15 '15 at 20:51
  • Oh yes, also Country Code. Thanks – William T Froggard Nov 15 '15 at 21:01
  • I edited my post above and put all the details – Knows Not Much Nov 15 '15 at 21:08
  • Okay so, your connection is strong. It must be something else. What brand of router do you have? – William T Froggard Nov 15 '15 at 21:10
  • OK. I have a second 13 inch mac book pro and even that says 56.53 Mbps on speedtest.net. but only my 15 inch mac book is slow – Knows Not Much Nov 15 '15 at 21:17

Excellent work with the details. The transmit rate and MCS index indicate that your mac has a high-speed connection to your router and that it's not an interference issue.

My next step would probably be timing me file transfer using Wi-Fi from the Mac to the PC or vice versa. You can enable filesharing on the Mac quite easily. download some YouTube movie from the Internet so that you've got something that will take 15 to 30 seconds to transfer so you can time it with the stopwatch.

It's hard to guess whether flash that runs the speed test.net simply running slow or you've actually got a legitimate speed issue with the Mac.

You'll also want to watch the activity monitor and the console application to see if you have io errors and if the network throughput matches the disk io which should all matching your benchmarking test.

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