Paint Calculator
Enter your room size, the number of doors and windows and how many coats you plan to get the gallons of wall paint to buy.
Your numbers
How we calculate it
Wall area = 2 × (length + width) × ceiling height. The calculator subtracts about 20 square feet per standard door and 15 per window, then multiplies the paintable area by the number of coats and divides by the coverage per gallon.
Most interior paints list a coverage of roughly 350 to 400 square feet per gallon on smooth, primed walls.
Assumptions and limits
- Ceilings, trim, closets and primer are not included.
- Textured or porous walls, dark-to-light color changes and deep colors may need more paint or more coats.
- Buy a little extra so all walls come from the same batch for consistent color.
Frequently asked questions
How much paint do I need for a 12x14 room?
With 8 ft ceilings, one door, two windows and two coats, a 12 by 14 foot room needs a bit over 2 gallons. Round up to 3 gallons or buy 2 gallons plus a quart.
Do I need primer?
Use primer on bare drywall, stains, patched areas or when making a big color change. Primer improves coverage and may reduce the number of paint coats.
What is the coverage of a gallon of paint?
About 350 to 400 square feet per gallon is typical. Check the can for the exact figure.
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Worked example (a fixed example using the starting numbers, it does not change as you type)
Inputs: Room length (feet) = 14; Room width (feet) = 12; Ceiling height (feet) = 8; Number of doors = 1; Number of windows = 2; Number of coats = 2; Coverage per gallon (sq ft) = 350.
- Paint needed 2.25 gallons
- Paintable wall area 366 sq ft
- Exact gallons 2.09
- Gallons to buy (whole cans) 3
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