Exterior Paint Calculator — How Much Paint for a House
Estimate how many gallons or litres of exterior paint your house needs from its size, gables, doors, windows, coats and the coverage on the can.
Guessing usually means a second trip to the store. This calculator works out the paintable wall area of a house — the four walls plus the triangular gable ends, minus doors, windows and anything you are not painting — and turns it into gallons or litres for the number of coats you plan, using the coverage printed on your paint.
How to use this tool
- Choose feet and gallons or metres and litres.
- Enter the length and width of the house and the wall height up to the eaves.
- Pick the number of gable ends and their height from the eaves to the roof peak.
- Enter how many doors and windows there are, plus any other area you will not paint.
- Set the number of coats and the coverage from the can, then read the amount to buy.
Formula
Wall area = 2 × (length + width) × height
Gable area = gables × ½ × width × gable height
Paint = (walls + gables − openings) × coats ÷ coverage × (1 + extra %)
Coverage is the area one gallon or litre covers in one coat. Doors are counted as 21 sq ft (3 × 7 ft) and windows as 15 sq ft (3 × 5 ft); in metric mode 1.9 m² and 1.4 m². The extra covers texture, spills and touch-ups.
Example
A 40 × 30 ft house with 10 ft walls has 2 × 70 × 10 = 1,400 sq ft of wall. Two 6 ft gables add 2 × ½ × 30 × 6 = 180 sq ft. Taking off 2 doors (42 sq ft) and 12 windows (180 sq ft) leaves 1,358 sq ft. Two coats at 350 sq ft per gallon need 7.76 gallons, and with 10% extra that is 8.5 gallons — buy 9: one 5-gallon bucket and four 1-gallon cans.
Frequently asked questions
How much exterior paint does a 2,000 sq ft house need?
Floor area is not wall area, so measure the outside walls. A two-storey home with a 25 × 40 ft footprint (2,000 sq ft of floor) and 18 ft walls has 2 × 65 × 18 = 2,340 sq ft of wall — about 13.4 gallons for two coats at 350 sq ft per gallon, before gables, openings and the extra allowance.
Do I really need two coats?
Two coats are usual when changing colour or painting weathered siding; one may be enough when repainting the same colour over sound paint. Follow the advice on the can.
Why does stucco or brick need more paint?
Rough, porous surfaces have more real surface area and soak up paint, so the coverage per gallon drops. Lower the coverage figure or raise the extra percentage for these surfaces.
Last updated: 2026-10-30