Paint Calculator
Estimate paint gallons needed for a room, minus doors and windows.
You need approximately
2 gallons
- Paintable wall area
- 269 sq ft
- Total area with 2 coat(s)
- 538 sq ft
How we calculate this
Paintable area = (wall length × wall height) − (doors × 21 sq ft) − (windows × 15 sq ft), multiplied by the number of coats. Gallons needed = paintable area ÷ coverage per gallon (350 sq ft is a standard mid-range estimate for most interior paints).
Example
Measuring tips
Measure the total perimeter of the room (add up all four walls) and the ceiling height. Standard interior doors are about 21 sq ft and standard windows about 15 sq ft — use the defaults above or enter your own measured openings for a more exact figure.
Common mistakes
- Forgetting to account for a second coat, which roughly doubles the paint needed.
- Using exterior paint coverage rates for interior paint, or vice versa — coverage varies by product.
- Not subtracting doors and windows, which can overestimate gallons needed by 10-15%.
Frequently asked questions
How many gallons of paint do I need for one coat on a 12x12 room?
A 12x12 room with 8 ft walls has about 384 sq ft of gross wall area. After subtracting typical doors/windows, expect roughly 1 gallon per coat at standard coverage.
Does primer count as a coat?
No — primer is calculated separately. This calculator estimates topcoat paint only; add primer gallons on top if the walls are unprimed or a color change requires it.
Related calculators
Estimates are provided for planning purposes. Actual material requirements may vary based on supplier specifications, compaction, site conditions, installation method, waste, and local code.