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Paint Calculator
Measure one room, subtract doors and windows, choose the number of coats, and get a whole-gallon shopping estimate.Plan your paint purchase
Change any measurement. Your estimate updates instantly.
2.09 gallons calculated before rounding
- Paintable area
- 365 ft²
- Area with coats
- 730 ft²
- Estimated paint cost
- $126
Calculated in your browser. Measurements are not uploaded or saved.
How this estimate works
Wall area minus 40 ft² for openings, × coats, divided by 350 ft² per gallon.
Measure twice and use the same unit throughout. Product coverage, material density, installation patterns, and local requirements can change the quantity you need.
Quick answer
To estimate paint, calculate the wall area, subtract doors and windows, add the ceiling if needed, multiply by the number of coats, then divide by the coverage printed on the paint can. Round the final amount up to a package size you can buy.
Worked example
A 12 × 10 ft room with 8 ft walls, 40 ft² of openings, two coats, and 350 ft²/gal coverage needs ((44 × 8 − 40) × 2) ÷ 350 = 1.78 gallons, before rounding to purchasable cans.
Assumptions
- Dimensions describe a rectangular room.
- Coverage is 350 ft² per gallon unless replaced with the product label value.
- Primer and application loss are not included.
How many gallons of paint do I need?
Start with the room perimeter: twice the length plus twice the width. Multiply that perimeter by wall height. This calculator subtracts 21 square feet for each door and 15 square feet for each window, then applies the number of coats. The default coverage is 350 square feet per gallon, but the product label should replace that default whenever you know it.
Should I include the ceiling?
Turn on the ceiling option only when the ceiling will use the same paint estimate. Its area is room length multiplied by room width. If the ceiling uses a different product or color, run a separate estimate so the shopping quantities stay clear.
Why can the actual amount change?
Bare drywall, porous masonry, textured walls, a major color change, and application losses can all reduce effective coverage. Primer is a separate product and is not included here. Keep the exact-gallon result for comparison, but buy based on available can sizes and the paint maker's instructions.
Last reviewed September 22, 2026. Source: EPA guidance on estimating paint and reducing leftover paint. Product instructions take priority over a general estimate.
Common questions
Short answers for the measurement details people most often need before using this calculator.
How much paint do I need for walls and a ceiling?
Enter the room dimensions, enable the ceiling, subtract doors and windows, and select the number of coats and coverage per gallon.
Can I calculate ceiling paint from square feet?
Yes. Ceiling area is room length multiplied by width. The calculator adds that area before applying coats and paint coverage.