Paint Calculation Formula
Perimeter = 2 x (length + width). Wall area = perimeter x ceiling height. Subtract: doors (21 sq ft each) and windows (15 sq ft each). Multiply by number of coats to get total paintable area. Divide by coverage per gallon and round up to the nearest half-gallon or quart. Add 10% for waste.
Frequently Asked Questions
One gallon of paint typically covers 350-400 square feet for smooth surfaces and 200-300 square feet for rough or porous surfaces like brick or bare drywall. This calculator uses 350 square feet per gallon as the standard coverage rate, which you can adjust.
One coat is sufficient for repainting a similar color. Two coats are recommended for color changes, dark-to-light transitions, fresh drywall, or for maximum durability. Three coats may be needed for very dramatic color changes or high-traffic areas.
Calculate the perimeter of the room, multiply by the wall height to get total wall area, then subtract the area of doors (approximately 21 square feet each) and windows (approximately 15 square feet each). Divide the net area by the coverage per gallon and multiply by the number of coats.
Yes, always buy 10-15% extra to account for spills, touch-ups, and variations in surface texture. Keep the extra sealed in the can for future touch-ups; note the color code and manufacturer on the label. Paint stored properly can last 2-5 years.
Primer is recommended for new drywall, significant color changes (especially covering dark colors), stain coverage, and surfaces that have never been painted. Using primer reduces the number of paint coats needed and improves adhesion. If using paint-and-primer-in-one, an extra coat often replaces a separate primer application.
Related Calculators
More tools in the Construction category.