Measure your space
Measure the room length, width, and height. Subtract the wall area of doors and windows, enter the number of coats, and use the coverage printed on your chosen paint.
Measure only the surfaces you will paint. For a rectangular room, multiply the perimeter by wall height, then subtract openings. Add ceilings or other surfaces separately rather than treating floor area as wall area. Keep the units consistent: square feet with square feet per gallon, or square metres with square metres per litre.
Worked example
Example: a 14 × 11 ft room with 8 ft walls has 400 sq ft of wall area. Subtract 42 sq ft of openings: 358 sq ft. Two coats cover 716 sq ft. At 350 sq ft per gallon, the estimate is 2.05 gallons: round up to 3 one-gallon cans. At an example shelf price of $38 per can, that is $114.
The formula
Wall paint quantity = [2 × (length + width) × height − openings] × coats ÷ coverage per unit.
Before you buy
Use the paint label for coverage and coats. The example prices are illustrative; FixCalc uses the price you enter.
Round the purchase amount up to the pack size sold by your chosen brand. Three one-gallon cans are different from buying one five-gallon bucket. Coverage on a label is a starting input; surface texture, colour changes, and the product instructions can affect the final quantity.
Keep the result in FixCalc
FixCalc is free to download. All calculators and complete results are free. Free saves up to 3 estimates in 1 project. FixCalc Pro Lifetime is one purchase for unlimited projects and saved estimates plus shopping-list PDF export.