what is the sq. ft. size of the apartment,is it existing or new construction, what are all the connected load(is thier gas available, does it have electric stove and grill, does it have electric heating, what are all the connected loads, is it air conditioned, how much light fixtures do you have, how many outlets, does it have electric washer and dryer, does it have a garage with an electric door opener),is it located in the USA? It could be 100 amp to 400 amps or more.