Open your YouTube test results by finding the entry under the External node and clicking:
This entry will not be here if you have disabled the YouTube test.
Once opened you can see the throughput results in the bottom right chart:
According to Google's Video Quality report (https://www.google.com/get/videoqualityreport/#methodology), you can interpret this throughput measurement in the following manner:
> 2.5 Mbps, HD streaming: Minimum throughput required to sustain an average YouTube HD video playback at 720p resolution
0.7 to 2.5 Mbps, SD streaming: Minimum throughput required to sustain an average YouTube SD video playback at 360p resolution
< 0.7 Mbps, LD streaming: Throughput too low to sustain YouTube SD video playback at 360p resolution