Paint Calculator
Buy the right amount of paint the first time.
Your numbers
Your results
Gross wall area (sq ft)
Gross wall area (sq ft)
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Paintable area (sq ft)
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Gallons needed
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Gallons to buy (rounded up)
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Paint Calculator by TheCalcTools
How the Paint Calculator works
Enter the room dimensions and wall height.
A standard door is taken as 20 sq ft and a window as 15 sq ft and both are subtracted.
Paintable area × coats ÷ coverage per gallon gives the paint needed.
The formula
Wall area = 2 × (length + width) × heightPaint = (wall area − openings) × coats ÷ coverage
Worked example
Using the default values shown in the calculator:
| Room length (ft) | 14 |
|---|---|
| Room width (ft) | 12 |
| Wall height (ft) | 8 |
| Doors | 1 |
| Windows | 2 |
| Coats | 2 |
| Coverage per gallon (sq ft) | 350 |
- Walls: 2 × (14 + 12) × 8 = 416 sq ft.
- Less 1 door and 2 windows leaves 366 sq ft; two coats need 2.09 gallons, so buy 3.
Result:
| Gross wall area (sq ft) | 416 |
|---|---|
| Paintable area (sq ft) | 366 |
| Gallons needed | 2.09 |
| Gallons to buy (rounded up) | 3 |
Frequently asked questions
How much does a gallon cover?
Most paints cover 350–400 sq ft per gallon on smooth, primed walls. Rough or dark surfaces need more.
Should I paint the ceiling too?
The ceiling is not included. Use the room area calculator for its size and add it separately.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.