Paint calculator
Enter the size of a room, how many doors and windows it has, and the coverage on the can to see how many gallons of paint the walls need, with the ceiling if you add it.
Doors and windows are taken off the walls only. The ceiling gets the same coats.
How it works
The walls are the distance around the room times the ceiling height: two times the length plus the width, times the height. The calculator takes the doors and the windows off that. It starts with 20 square feet for a door, which is about 3 by 6.7 feet, and 15 for a window. Both are starting values, so measure yours.
If you tick the ceiling, it adds the floor area of the room. Then it multiplies the area to paint by the number of coats, divides by the coverage of a gallon, and rounds up to whole gallons.
The coverage figure
The can tells you how far a gallon goes, and that figure is the one to use. Guides give about 350 to 400 square feet a gallon for each coat on smooth walls, and less on rough or porous ones. The calculator starts at 350, the cautious end, so that you are less likely to run short.
A worked example
A room 12 feet by 14 feet with 8 foot walls has 416 square feet of wall. One door takes off 20 and two windows take off 30, which leaves 366 square feet to paint.
Two coats is 732 square feet. At 350 square feet a gallon that is 2.09 gallons, so you buy 3. Add the ceiling, 168 square feet, and the total is 534, or 1,068 for two coats. That is 3.05 gallons, so you buy 4.
What it leaves out
The calculator counts the walls and, if you ask, the ceiling. Trim, closets and primer are not in it.
Questions
How much paint do I need for a 12 by 14 foot room?
With 8 foot walls, one door, two windows and two coats, the walls come to 366 square feet and need 2.1 gallons, so buy 3. With the ceiling too it is 4 gallons.
How many square feet does a gallon of paint cover?
The can tells you, and that figure is the one to use. Guides give about 350 to 400 square feet for each coat on smooth walls. The calculator starts at 350.
Do I paint the ceiling too?
Tick the box and the calculator adds the ceiling, which is the floor area of the room. It gets the same number of coats as the walls.
Why does the calculator round up?
Paint is sold by the can, so the calculator rounds up to whole gallons. It shows the exact figure too, so you can see how close to a gallon you are.
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