ATHENA CALCULATORS
How Much Paint Do I Need?
Estimate how many gallons of paint you need for walls, ceilings, doors, and windows. Enter room dimensions, the number of coats, and the coverage printed on your paint can to plan your purchase.
How the paint calculator works
The calculator estimates wall area from the room perimeter and wall height, subtracts approximate areas for doors and windows, optionally adds the ceiling area, multiplies by the number of coats, and divides by coverage per gallon.
Wall area = 2 × (length + width) × wall height
Paint needed = paintable area × coats ÷ coverage per gallon
Worked example
For a 12 ft × 10 ft room with 8 ft walls, the gross wall area is 352 square feet. After subtracting approximate door and window areas, the paintable area is lower. At 2 coats and 400 square feet of coverage per gallon, the calculator converts the resulting area into gallons and adds a 10% planning allowance for the recommended order.
What coverage should I use?
Use the coverage printed on the exact paint product when available. A common planning range is roughly 350–400 square feet per gallon, but actual coverage varies with the paint, surface texture, color change, application method, and number of coats.
Should I paint the ceiling?
If the ceiling will be painted, include it in the estimate. The calculator adds the room's floor-area footprint when the ceiling option is selected. Ceiling coverage and product requirements can vary, so confirm the paint manufacturer's guidance.
Doors and windows
The calculator uses approximate areas for doors and windows to avoid counting those surfaces as full wall area. For an unusual door, large window, or extensive opening, use a more precise measurement if you need a tighter estimate.
Why order extra paint?
The recommended order includes a 10% planning allowance for touch-ups, waste, and normal variation. Your actual requirement may be higher or lower depending on the surface and product.
Important planning note
This calculator estimates paint quantity and is not a substitute for the coverage information supplied by the paint manufacturer. Primer is not included in the estimate and should be calculated separately when needed.