Question:

I was wondering if a man can wear 3/4-trousers (longer than shorts covering the legs till the middle of the calves) in Iran or do the legs have to be fully covered?

Answer:

In general, the code of dressing in Iran for men is not as rigid as the women, long trousers covering up to ankle, long-sleeved or Short-sleeved shirts and sandals are acceptable. But it prohibits 3/4 trousers and shorts, although you may not be laughed at by the public, the police may warn you and advise to change your dress.
It is common for the Iranian guys to wear 3/4 trousers outdoors but of course not in the cities.

Check cheap Iran tours.