About the Paint Calculator
Buying the right amount of paint saves money and trips to the store. This estimator turns a room's dimensions into the paintable wall area, applies your number of coats, and rounds up to whole gallons — subtracting doors and windows so you don't over-buy.
How it’s calculated
Wall area = 2 × (length + width) × height. Paintable area subtracts doors and windows. Gallons = (paintable area × coats) ÷ coverage per gallon (about 350 sq ft per coat), rounded up to whole cans.
Example calculation
A 12 ft × 10 ft room with 9 ft ceilings has about 396 sq ft of wall. For two coats at 350 sq ft per gallon, that's roughly 2.3 gallons — so you'd buy 3 one-gallon cans.
Frequently asked questions
How many square feet does a gallon of paint cover?
About 350 square feet per coat is typical, though it varies by paint and surface. Check the can — porous or textured walls absorb more.
Should I subtract doors and windows?
For a closer estimate, yes. Enter their combined area to remove it from the paintable surface. For a quick estimate you can leave it at zero and buy a little extra.
How much extra should I buy?
Rounding up to whole cans usually leaves enough for touch-ups. For big color changes or dark-over-light, plan on an extra coat.
This is a general material estimate for planning only. Actual quantities vary with waste, offcuts, site conditions, product coverage, and technique. Confirm measurements and coverage rates before ordering, follow local building codes, and round up — running short mid-project is costly.