How this calculator works
Estimate a practical paint quantity before you buy. The calculator subtracts openings, applies the number of coats, adds a waste allowance and rounds the result into purchase-friendly gallons.
Paintable wall area = perimeter × wall height − door area − window area. Gallons = area × coats × (1 + waste) ÷ coverage.
Example
A 12 × 10 ft room with 8 ft walls, one door, two windows and two coats needs about 2–3 gallons at typical coverage.
Reliability check
Measure every wall at finished height, then compare the calculated gallons with the coverage printed on the exact paint and primer selected. A strong color change, porous repair or textured wall can require another coat.
How to get a better estimate
- Measure each room instead of estimating from floor area alone.
- Use the coverage printed on the specific paint can whenever possible.
- Add more waste for textured walls, color changes or porous surfaces.
What the result means
Paint coverage changes with wall texture, porosity, primer, application method and color change. Use the coverage printed on the exact paint product and measure unusual openings instead of relying on averages.
Reference tables
Compare your room with the paint table to check wall area, coats and whole-gallon rounding before changing product coverage.