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HeizerDesk Paint Calculator
Enter the room's dimensions and how many coats you're putting on. This gives you the paintable wall area with doors and windows deducted, and the gallons to buy. Use it as a free Paint Calculator on site — the working is shown underneath, not hidden.
Your numbers
Result
Paint needed
2.09
gallons
- Round up to buyTo the nearest quart
- 2.25gallons
- Paintable area
- 365sq ft
- Total area across all coats
- 730sq ft
- Gross wall area
- 416sq ft
- Deducted for openings
- 51sq ft
How this is calculated
- Wall area = 2 × (length + width) × ceiling height.
- Deductions = 21 sq ft per door, 15 sq ft per window — the standard allowances for a 3′×7′ door and a 3′×5′ window.
- Ceiling, if painted = length × width.
- Total area = paintable area × number of coats.
- Gallons = total area ÷ coverage per gallon.
Before you order
- Primer is a separate calculation. Bare drywall, patched repairs, or going light over dark all need one, and primer covers roughly the same area per gallon.
- Deep bases and strong colours often need three coats to look right, not two.
- Trim, doors and window casings are usually a different sheen and a different can — this figure is walls and ceiling only.