Figure out how many gallons of paint you need for your room walls.
How this worksTotal wall area is 2 × (length + width) × ceiling height. We subtract about 20 sq ft per door and 15 sq ft per window (paint-free areas), then multiply by the number of coats. One gallon of paint covers roughly 350 sq ft, so we round the gallons up — you can't buy a fraction of a gallon at the store.