Wall paint calculator
Estimate wall paint from room dimensions, measured openings, coats and product coverage. Separate base gallons, extra paint, can count and purchased surplus.
How to use this tool
Replace the example values with your own, then choose Calculate paint. Changing an input clears the previous result until you calculate again. Copy the result or download a CSV to keep a record.
Method
Gross wall area = 2 × (room length + room width) × wall height. Subtract your measured total opening area. Paint gallons = remaining wall area × coat count ÷ product coverage. Add your extra percentage, then round up to whole cans of the selected capacity.
Worked example
A 12 × 10 ft room with 8 ft walls has 352 sq ft of walls. Subtract 42 sq ft of openings for 310 sq ft. Two coats at 350 sq ft/gal need about 1.7714 gal; adding 10% gives about 1.9486 gal, so buy two 1-gallon cans.
Assumptions and limits
Walls only: estimate the ceiling, trim and primer separately. Measure doors and windows instead of relying on fixed deductions. Use your product’s coverage for the actual surface. Texture, porosity, application losses and color changes affect the final amount. If openings cover the entire wall area, the estimate is zero.
Reference: Benjamin Moore: paint calculator.