To find the throughput on your connection, you need to test it directly from the source, so to speak.
If you can, plug a computer directly into the gateway and test the speed there. Here are a couple of different testers I use, fast.com and the googlefiber one will work on any device (tablets and smartphones too!) without having to download any apps/software -
- http://www.fast.com
- http://speed.googlefiber.net
- http://beta.speedtest.net
- http://myaccount.cox.net/internettools/speedcheck/speedcheck.cox
The main reason I recommend testing with a computer directly plugged in, is that wifi is so variable. For example, using a Galaxy S5 I just got a 30Mbps down on wifi. Using a laptop (on wifi) right next to it I got a 120Mbps - both devices less than a foot from each other and 1 room away from the router. If I plug directly in, I usually get between 120Mbps and 180Mbps (not always though, I have my occasional speed issues too!).