Paint Calculator
Estimate paint for any room. Enter the wall dimensions, subtract windows and doors, choose your number of coats, and get the paintable area, gallons required, and an estimated cost.
Updated June 2026 · Free · No sign-up
Your project
Estimate
2gal
Paint needed · Rounded up to whole gallons
- Paintable wall area
- 333ft²
- Estimated paint cost
- $76.00
Estimates are guidance only and exclude tax, labor, and site conditions unless stated. Confirm with a local pro.
How it's calculated
No black boxes — here is the exact math behind your estimate, so you can check it or adapt it for your own quote.
- 1
Wall area = 2 × (length + width) × height - 2
Openings = windows × 15 + doors × 21 - 3
Paintable area = wall area − openings - 4
Gallons = ⌈ paintable × coats ÷ 350 ⌉
Worked example
A 12 ft × 12 ft room with 8 ft walls, 2 windows, 1 door, painted with 2 coats.
Inputs
- Room length
- 12 ft
- Room width
- 12 ft
- Wall height
- 8 ft
- Windows
- 2
- Doors
- 1
- Coats
- 2
- Price per gallon
- 38 $/gal
Result
- Paint needed
- 2 gal
- Paintable wall area
- 333 ft²
- Estimated paint cost
- $76.00
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Frequently asked questions
How much does a gallon of paint cover?
About 350 square feet per coat for most interior wall paints. Rough or porous surfaces and bold color changes cover less, so two coats are the safe default.
Do I count the ceiling?
This calculator estimates walls only. For a ceiling, run the room length × width as a separate area and add it at the same coverage rate.
Why round up to whole gallons?
Paint is sold by the gallon (or quart), and you want a little extra for touch-ups and a consistent color batch. We round up and recommend keeping the leftover.