The tings that Fabio said are right but incomplete. The Erlang is unit for Traffic Intensity, not for Traffic Volume. There is an unit called Erlang/Hour (In that case Fabio is correct) that shows the Traffic Volume. If you have traffic measurements for all day in Erl you must calculate first the Traffic Volume in minutes. The number needed for multipliing the Erlangs is corresponding to the observed period.
If the measurement is over 15 min and you have 10 Erl, hence multiply 10*15=150 min, if the period is 24Hour and you have for the whole period 10Erl, then 10*24*60=14400 min.
On the other hand there is something else. You have the measurements for the holding time, not for the converstaion time. The users pay for conversation not for holding the line. If B-(Busy, not answer and so on) A-subscriber is not charged, but will generate traffic.
I’dont know how your subscribers are charged, but in my country they are charged at least for a minute and after that for every second. So if a call is shorter than 1 min they will pay for a whole, but the generated traffic will be less.