Paint Calculator
Walls, rooms & coats
Avoid buying too much (or too little) paint. This free paint calculator estimates the gallons or liters you need based on room dimensions, ceiling height, coats and openings like doors and windows — so your next project goes on smoothly the first time.
Formula
Wall area = perimeter × height − openings. Paint = (area × coats) ÷ coverage.
Frequently asked questions
▸How much paint do I need per room?
One gallon covers about 350 ft² (32 m²). Multiply wall area by coats, then divide by coverage.
▸Should I subtract doors and windows?
Yes — subtract about 21 ft² per door and 15 ft² per window for accuracy.
Example calculations
Wall area ≈ 384 ft² minus 1 door and 2 windows = 348 ft². With 350 ft²/gal coverage and 2 coats, you'll need about 2 gallons.
Walls ≈ 576 ft² minus openings = 525 ft². Two coats at standard coverage = roughly 3 gallons.
180 ft² × 2 coats ÷ 350 = 1.03 gallons. One gallon plus a quart for touch-ups is ideal.
Paint Calculator FAQ
▸How much paint do I need for a 12x12 room?
A 12×12 ft room with 8 ft ceilings needs about 2 gallons for two coats after subtracting one door and two windows.
▸How much does a gallon of paint cover?
Standard interior latex paint covers about 350 ft² per gallon (32 m² per liter). Rough or porous surfaces may cover less.
▸Do I need to subtract doors and windows?
Yes. Subtract about 21 ft² per door and 15 ft² per standard window for an accurate estimate.
▸How many coats of paint should I apply?
Two coats is standard. Use a primer first when going from dark to light, painting over stains or covering new drywall.