Paint Calculator
Estimate gallons from wall perimeter, wall height, openings and coats.
Project inputs
Enter your measurements. Results update automatically.
Need to price the whole job?
Move from quantity math to materials, labor, overhead, markup and profit with Nails & Numbers contractor tools.
See estimating toolsHow many gallons of paint do I need?
This calculator estimates paint from wall perimeter, wall height, openings, number of coats and the coverage rate you enter. It subtracts the opening area before multiplying by coats, then divides by the selected square-feet-per-gallon coverage.
Paint formula
(Perimeter × wall height − openings) × coats ÷ coverage per gallon = gallons. The calculator also rounds up to a whole-gallon planning quantity.
Use the product's coverage
Coverage varies with paint, primer, surface texture, porosity and application method. Use the manufacturer's stated coverage when available instead of assuming every paint covers the same area.
Doors, windows and multiple coats
Enter the combined area of openings you do not plan to paint. Two coats roughly double the paintable square footage used in the calculation, while primer should be estimated separately if it has a different coverage rate.
Common paint calculator questions
Should I subtract every window and door?
For a planning estimate, subtract openings you do not intend to coat. Small openings may not materially change the order, especially when extra paint is useful for touchups.
Why does coverage vary?
Rough or porous surfaces can consume more paint than smooth, sealed surfaces, and different products publish different coverage ranges.
Does the calculator include ceilings?
No. Add ceiling area separately if the ceiling will be painted.