How much should you wash your face per day?

Twice a day: Most important time to wash is at the end of the day to wash off the dirt and oil buildup and makeup and sunscreen. If you take a shower in the morning you're already washing your face. Most people don't need a deep cleansing in the morning but just a mild rinse or gentle cleanser. Also good to wash your face after working out and sweating. Don't overscrub your skin.

Depends: It really depends on your type of skin (oily, dry, using makeup). Most people probably do just fine by washing their face once or twice per day. Over washing can also surprisingly dry your face. You might get a more in depth answer by seeing a dermatologist.