# How to calculate the blocking probability of processes with gamma-distributed service times using the Erlang formula?

I have seen numerous examples of using the Erlang formula to calculate the blocking probability for processes with exponentially distributed service times. However, I am not quite sure how to do that for a distribution which is not exponential, e.g. gamma.

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 It seems to me that you'd have to derive a new formula, since the Erlang formula is derived with the fixed assumption of exponentially distributed runtimes (note: that's not the same as exponential!). – Raphael♦ Nov 20 '12 at 9:08