Justin, in case this might help you:
1 Erlang means 1 unit of equipment (e.g. 1 channel in a circuit) fully occupied for 1 hour. So if a trunk circuit carries 10 calls, each lasting 6 minutes, it has carried 1 Erlang. The method I use to dimension trunk circuits is to multiply the average call duration (or estimated duration if this is a new operation) by the number of calls in the busy hour, and divide by 60. This may not be terribly scientific, but it gives a very close approximation. Hope this helps.