To calculate the cost per square foot of painting a house, you’ll need to start by calculating the area of the surfaces you plan to paint. In addition to factoring in the price of the paint you’ll need to cover each area, you’ll also have to consider the cost of your tools. If you’re bringing in a professional, they’ll charge you for their labor as well as supplies.
1. Multiply the house perimeter by the roofline height to measure the exterior
• To calculate the area of exterior walls, measure the perimeter of the house, or the combined length of all exterior walls. Exclude porches or other “appendages.” Multiply the perimeter by the height of the roofline, or the spot where the top of an exterior wall meets the roof. If your house has gables (peaked parts of the roof), add half the height of a story to the total roofline height to get a ballpark approximation of the area including gables
• Most houses have a height of 9 feet (2.7 m) per story. Add 4.5 feet (1.4 m) to account for any gables.
• For example, if your house is 24 feet (7.3 m) by 35 feet (11 m) and 2 stories tall, the area in square feet would be (24 + 24 + 35 + 35) x (9 + 9 + 4.5) = 118 x 22.5 = 2,655.
2. Multiply a room’s perimeter by the ceiling height to find the wall area.
• To estimate the cost of painting a room, find the total wall area of the room. Measure the perimeter of the room (the combined lengths of all sides of the room) and multiply it by the height of the ceiling.
• For example, if the perimeter of your room is 55 feet (17 m) and the ceiling is 10 feet (3.0 m) high, the area of the walls is 550 square feet (51 m2).
• If the room has any doors and windows, measure the area of each and subtract it from the wall area for a more accurate estimate. Multiply the length of each door or window by its width to find the area.
3. Measure the area of the ceilings if you plan to paint them.
• If you’re going to paint your ceilings, you’ll need to factor them in as well. Measure the length of the ceiling and multiply it by the width to get the total area.
• For example, if the ceiling is 12 feet (3.7 m) by 10 feet (3.0 m), the area is 120 square feet (11 m2).