For easy understanding:
if you have 5 calls in 1 hour, with MHT (mean holding time) of 120 sec, it gives
5*120/3600=0,16666666Erl traffic
For proper dimensioning, some other erlang calculations must be done, with some other parameters, i.e. blocking probability etc.
Of course, maximum traffic in Erlangs recommended is differet from trunk to trunk ( it depends for what type of signalization is used)
BR
Ivan