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
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.
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.
What if I am painting the ceiling?
If the ceiling will use the same paint, include it in the estimate rather than treating the wall result as the complete project quantity. A ceiling adds the room's floor-area dimensions to the paintable surface.
How do doors and windows affect the estimate?
Openings reduce the amount of wall surface that needs paint, but their exact dimensions vary. ATHENA uses planning deductions for standard door and window areas; for unusual openings or large glass areas, treat the result as an estimate and adjust as needed.
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. For more detail, see Paint Coverage Calculator Guide or Paint Coverage Per Gallon Guide.
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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