A gallon of paint covers a maximum of 400 square feet in wall space. To determine how much paint is needed for a one-bedroom apartment, first estimate the total square footage of the walls to be painted.

To determine the total square footage of the walls in an apartment, first measure the total distance around each individual room and add the totals for each room together. Then, multiply the total perimeter by the height of the walls. From this number,subtract 21 square feet for each door and 15 square feet for each window. Divide the resulting total square footage by 400 for an estimate of the number of gallons of paint needed to cover the apartment.