Exterior House Paint Calculator
By Vinod Kondeti · Updated
Exterior walls are the perimeter times the height up to the eaves, plus the triangular gable ends under the roof peaks. Rough siding, stucco and bare wood absorb more paint than smooth walls, so use the coverage on your exterior product's label and lower it for rough surfaces.
How do I measure for a exterior project?
- Walk the house with a tape and add up every wall for the perimeter.
- Gable area = ½ × gable width × height from the eave line to the peak.
- Trim, doors and shutters are usually a different paint. Leave them out here.
How is the exterior amount calculated?
- Room walls = 2 × (length + width) × height − doors & windows (+ length × width for the ceiling)
- Gallons = area × coats ÷ coverage per gallon (default 350 ft²)
- To buy = gallons rounded up to whole quarts (4 qt = 1 gal)
- Exterior = perimeter × wall height + gables × ½ × width × height − openings
- Openings = doors × area per door + windows × area per window + other
- Primer (optional) = one coat: area ÷ primer coverage
- Cost = whole gallons × your $/gal (paint + primer)
Exterior calculator questions
How much paint for a 140 ft perimeter, 10 ft walls, two 30 × 6 gables, 2 doors and 10 windows, 2 coats?
1,400 + 180 − (2 × 21 + 10 × 12) = 1,418 ft², and × 2 ÷ 350 = 8.10 gal, so 8 gallons + 1 quart.
Why is exterior coverage lower?
Texture and porosity increase absorption. Benjamin Moore data sheets give coverage as a range, so stay at the low end for rough surfaces.
Sources
Estimates only. Use the coverage or bag size printed on your product. Read the paint guide for worked examples.