How much sunscreen should be used, and how often should it be applied?
It is recommended that sunscreen be applied in a quantity of about 2 milligrams per square centimeter of skin. For an average adult, this roughly translates to about one ounce (enough to fill a shot glass) to cover the body. Sunscreen should be applied 30 minutes before going outdoors and reapplied approximately every two hours or after swimming, sweating, or towel drying.