How much milk would you have to drink to get 500 mg of calcium?

My Gallon of milk says it contains 30% Calcium. Don't know if you found the volume of 30% of a gallon and convert to mgs, to find the answer?

Are we doing your homework with you?

Milk Matters Calcium Education Campaign (http://www.nichd.nih.gov/milk/prob/calcium_need.cfm)