Dashboard Metrics displays Dyno Load, measured as "1m Load Average" and "1m Load Max". The method of taking these measurements is explained on our Dev Center (https://devcenter.heroku.com/articles/metrics#dyno-load), but this does not illustrate what you should expect my application to run at.
Free, Hobby and Standard Dynos
Free, Hobby and Standard Dynos run on shared systems, and as such, you should aim to keep maximum Dyno load to within 0.5 and 1.0 to avoid any potential degradation of performance.
Performance Dynos are single tenant, this means that your Dyno will have full access to the resources on the system. For Performance-M Dynos, your should aim to keep your maximum Dyno load to within 3.0 and 4.0. For Performance-L Dynos, your should aim to keep your maximum Dyno load to within 12.0 and 16.0