To estimate the amount of paint you need in order to cover the walls of a room, add together the length of all the walls and then multiply the number by the height of the room, from floor to ceiling. The number you get is the room's square footage. Is that math class coming back to you now?
Use the following formula to estimate the amount of ceiling paint you need. Double the result if the ceiling requires two coats.
1. Multiply the length of the ceiling times its width to find its area.
12 × 24 = 288 square feet
2. Divide that number by 350 (the estimated square feet covered per gallon) to figure out how many gallons of paint you need.
288 ÷ 350 = .8
For this example, you want to buy 1 gallon of ceiling paint for a single coat.
Wall paint estimator
Use the following formula to estimate the amount of wall paint you need. Double the result if the walls require two coats.
1. Add together the length of each wall.
12 + 24 + 12 + 24 = 72 feet
2. Multiply the sum by the wall height, to find the total wall area.
72 × 9 = 648 square feet
3. Subtract 20 square feet for each door (20 × 2 = 40) and 15 square feet for each window (15 × 2 = 30) to find the actual amount of wall area you're painting.
648 – 70 = 578 square feet
4. Divide this figure by the paint coverage (350 square feet per gallon), and the result is the number of gallons to purchase.
578 ÷ 350 = 1.65
For this example, you can buy either 1 gallon and 3 quarts or just round up and buy 2 gallons of paint for a single coat.