Question: civ 5 how many units to take a city?
Answer: Use 2-3 Melee Units to act as your front line against the City. Your Ranged and Siege can attack from 2 hexes away. You need the Melee to actually take the City once its health has been depleted, so keep at least one at full health, else have a fast unit like a Horseman/Cavalry to run in when the City is at 0 Health.