Estimate paint needed
Wall dimensions in feet, coats, and openings to subtract.
How the paint calculation works
Multiply the total wall length (the perimeter of the room) by the ceiling height to get the gross wall area. Subtract about 21 square feet for each door and 15 square feet for each window to get the paintable area. Multiply by the number of coats, then divide by the coverage of one gallon, which is usually 350 to 400 square feet. The result is rounded up to whole gallons because paint is sold by the can.
Frequently asked questions
How much paint do I need for a room?
First find the wall area: add the lengths of all walls, multiply by the ceiling height, then subtract the area of doors and windows. Divide that paintable area by the coverage of one gallon, then multiply by the number of coats. One gallon typically covers about 350 to 400 square feet per coat.
How many square feet does a gallon of paint cover?
A gallon of interior wall paint usually covers about 350 to 400 square feet in one coat on a smooth, primed surface. Rough or unprimed surfaces absorb more and cover less, so buy a little extra.
How many coats of paint do I need?
Two coats is standard for an even finish and good color depth. One coat may be enough when repainting the same color, while bold or drastic color changes can need three coats.
Should I subtract doors and windows?
Yes. Doors and windows are not painted with wall paint, so subtracting their area gives a more accurate estimate. This calculator uses about 21 square feet per door and 15 square feet per window by default.
Is my data saved anywhere?
No. All calculations run entirely in your browser. Nothing you enter is uploaded or saved on a server.
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Disclaimer: Results are provided for general informational purposes only. Always double-check important figures independently.