Paint Calculator
Estimate interior wall paint including openings and coats.
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What this tool does
Estimate interior wall paint including openings and coats. Ceiling paint is excluded. Porous walls and color changes may need more coats.
How to use the Paint Calculator
- Enter or select room length in ft.
- Enter or select room width in ft.
- Enter or select wall height in ft.
- Enter or select door and window area in sqft.
- Enter or select number of coats.
- Enter or select coverage per gallon in sqft.
- Read the calculated result; change any measurement to compare alternatives.
Formula
paint gallons=max(0,2×(length+width)×height−openings)×coats/coverage
- length
- Room length (ft, before metric conversion)
- width
- Room width (ft, before metric conversion)
- height
- Wall height (ft, before metric conversion)
- openings
- Door and window area (sqft, before metric conversion)
- coats
- Number of coats
- coverage
- Coverage per gallon (sqft, before metric conversion)
Ceiling paint is excluded. Porous walls and color changes may need more coats.
Worked example
For paint calculator, the following measurements illustrate the exact method: Room length: 20; Room width: 12; Wall height: 8; Door and window area: 40; Number of coats: 2; Coverage per gallon: 350.
Inputs
- Room length20 ft
- Room width12 ft
- Wall height8 ft
- Door and window area40 sq ft
- Number of coats2
- Coverage per gallon350 sq ft
Result
- Gallons required2.7 gal
- Whole gallons to buy3
- Paintable wall area472 sq ft
Results explained
- Gallons required
- Gallons required from the formula above, expressed in gal before metric conversion. Ceiling paint is excluded. Porous walls and color changes may need more coats.
- Whole gallons to buy
- Whole gallons to buy from the formula above. Ceiling paint is excluded. Porous walls and color changes may need more coats.
- Paintable wall area
- Paintable wall area from the formula above, expressed in sqft before metric conversion. Ceiling paint is excluded. Porous walls and color changes may need more coats.
Frequently asked questions
Wall perimeter times height minus openings gives paintable area; multiply by coats and divide by coverage.
Enter room dimensions, openings, coat count and coverage on the can.
Use 5–10% for simple layouts and 10–15% for diagonal cuts or complicated outlines; the allowance is editable.
Split the outline into rectangles or triangles and calculate each section separately. Do not count overlapping sections twice.
This is a purchasing estimate, not a structural design. Confirm measurements and local requirements before buying or building.