Paint Calculator
Use this paint calculator to estimate how much paint a room needs. Enter the room size or wall lengths, the number of doors and windows, and the coats to get the paintable area and the gallons, quarts and liters required. Coverage defaults to 350 sq ft per gallon and can be changed.
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Wall area
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Doors and windows
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Area to paint (one coat)
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Total area to cover (all coats)
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Paint needed (gallons)
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Gallons to buy (rounded up)
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Quarts
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Liters
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Estimated cost (rounded-up gallons)
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Paintable area = wall perimeter × height − doors × door area − windows × window area (+ ceiling). Gallons = area × coats ÷ coverage. 1 US gallon = 4 quarts = 3.785 L. A coverage of 350–400 sq ft per gallon is typical for one coat on smooth walls; use the figure on your paint label for your product and surface. Cost uses whole gallons rounded up. In metric, 350 sq ft per gallon is about 8.6 m² per liter.
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How it works
- How do you calculate how much paint you need?
- Find the wall area (perimeter × height), subtract doors and windows, multiply by the number of coats, then divide by the coverage per gallon. A 12 × 14 ft room with 8 ft walls: 416 − 20 − 30 = 366 sq ft; × 2 coats ÷ 350 = 2.09 gallons.
- How many square feet does a gallon of paint cover?
- Paint makers such as Sherwin-Williams quote about 350–400 sq ft per gallon for one coat on a smooth, prepared surface. Rough or porous walls use more, so check the coverage printed on your can.
- How many coats of paint do I need?
- This calculator defaults to 2 coats, which you can change. Bare drywall or a big color change may also need primer, which is not included in the paint total.
- How much area should I subtract for doors and windows?
- The defaults are 20 sq ft per door and 15 sq ft per window, and you can enter your own. A 36 × 80 in door is about 20 sq ft, so the default is a rounded allowance.
- How do I include the ceiling?
- Tick the ceiling option to add the room length × width to the paint area. If the ceiling uses a different paint, run the calculator twice and keep the totals separate.