Paint Calculator
Buying the right amount of paint saves money and trips to the store. This calculator works from the wall area you measure, the number of coats you plan, and the coverage per gallon stated on your can. It returns the exact gallons required, the gallons rounded up to whole cans, the total surface area painted, and the estimated paint cost. Because coverage varies by product and surface, you enter it yourself rather than relying on an assumed value, keeping the result accurate to your specific job.
Paint quantity formula
Total area = wall area * coats
Gallons required = total area / coverage per gallon
Cans to buy = round up of gallons required
Cost = gallons required * price per gallon
The job needs enough paint to cover the wall area once per coat. Dividing the total area by the manufacturer's stated coverage gives the gallons; rounding up gives the whole cans you must buy.
Paint estimating tips
- Read the coverage figure from your specific paint can; it varies by product.
- Rough, textured, or unprimed surfaces absorb more and cover less.
- Dark colors over light walls usually need two coats.
- Always round up to whole cans and keep leftovers for touch-ups.
- One US gallon equals 3.785 liters under the international definition.
Paint calculator: frequently asked questions
How much area does one gallon of paint cover?
Coverage depends on the paint and surface, so this calculator asks you to enter it. Manufacturers typically state coverage on the can, often around 350 to 400 square feet per gallon for a smooth interior wall. Rough or porous surfaces cover less, so use the figure your product specifies.
How do I measure my wall area?
Multiply the width by the height of each wall and add them together. For a room, add the area of all four walls. You can subtract the area of large doors and windows if you want a tighter estimate, but many painters leave them in as a safety margin.
Why does the number of coats matter?
Each coat needs its own full coverage of paint, so two coats use roughly twice the paint of one coat. Dark colors over light walls, or new drywall, often need two coats. The calculator multiplies the area by the number of coats before dividing by coverage.
Should I round up the gallons I buy?
Yes. The calculator shows the exact gallons required, which is usually a fraction. Always round up to the next whole can so you do not run short mid-job, and keep any leftover for touch-ups. The exact figure helps you decide between can sizes.
How is the paint cost estimated?
Cost is the exact gallons required multiplied by the price per gallon you enter. For a real purchase, base your budget on the rounded-up number of cans, since you cannot buy a partial gallon. The cost output here reflects the precise paint volume needed.
Official sources
- U.S. National Institute of Standards and Technology: Units of measurement and area.
- U.S. Environmental Protection Agency: Safer paint and coating guidance.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.