Paint Calculator
How many gallons or liters of paint a room needs, from the wall size, doors and windows, coats and the coverage on the can.
How this is calculated
The wall area is the total width of the walls times their height, minus doors and windows. Measure each one as width times height: a common 32 by 80 inch interior door, for example, is about 17.8 square feet (1.65 square meters).
The paint needed is the area times the number of coats, divided by the coverage. Use the coverage printed on your can: most wall paints state between about 250 and 400 square feet per gallon. If you leave it empty, 350 square feet per gallon is used (8.6 square meters per liter, the same rate in metric).
Paint is sold in fixed sizes, so the result also shows how to buy it in gallons and quarts (a quart is a quarter gallon).
Limits
Walls only; ceilings and trim are separate jobs. Rough or porous surfaces such as new drywall, bare plaster, brick or a big color change soak up more paint, so use the low end of the can's coverage or add a coat.