How Much Paint Do I Need?

Estimate the gallons of paint needed for room walls and ceilings by using your dimensions, number of coats, and the coverage printed on your paint can.

Use the paint calculator first

Enter the room length, width, wall height, doors, windows, number of coats, and paint coverage in the ATHENA Paint Calculator. You can also include the ceiling when it will be painted with the same product.

How paint quantity is calculated

Wall area is calculated from the room perimeter and wall height. The calculator subtracts approximately 21 square feet for each door and 15 square feet for each window, then adds the ceiling area when selected.

The paint quantity is calculated from the paintable area, number of coats, and coverage per gallon:

Paint needed = paintable area × coats ÷ coverage per gallon

What coverage should I use?

Use the coverage printed on the paint can whenever possible. ATHENA starts with 350 square feet per gallon as its default planning value; the calculator lets you change that coverage to match your product.

Example: a 12 × 10 ft room with 8 ft walls

With one door, two windows, and two coats, the estimated paintable wall area is about 301 square feet before any ceiling is added. At 350 square feet of coverage per gallon, the calculated amount is about 1.7 gallons. ATHENA adds a 10% planning allowance to its recommended order.

Should I buy extra paint?

ATHENA adds a 10% planning allowance for touch-ups, waste, and normal variation. Your actual requirement can differ based on surface texture, color changes, application method, and the product you select.

Ready to calculate?

Run your own project numbers here: Free Paint Calculator.

Compare interior wall paint on Amazon (paid link)

Planning note

Paint coverage is a product-specific estimate. For the most accurate order, use the manufacturer's coverage information and account for the condition of the surface you are painting.

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