How much paint a house takes outside
The walls all the way round, times their height, less the doors and windows; times the coats, over what a gallon covers outside. A house 40 by 30 feet with 9 foot walls is 2 × (40 + 30) × 9 = 1,260 square feet. Two doors at 20 square feet and eight windows at 15 take 160 off: 1,100 square feet, and two coats at 350 square feet a gallon is 6.29 gallons. Buy a 5-gallon pail, a gallon can and two quarts for the walls, and a gallon of trim paint.
Add the gable ends as a triangle each. Two gables 30 feet wide and 8 feet to the peak are 30 × 8 ÷ 2 = 120 square feet each; with them the house is 1,340 square feet, 7.66 gallons — a 5-gallon pail and three gallon cans.
The 350 is the figure Sherwin-Williams' calculator works exterior walls at; Behr gives 250 to 400. If your can gives another figure, type it under Assumptions.
Measuring a gable end
A gable is a triangle: measure the width of the wall it sits on and the height from the top of that wall to the peak, and its area is half of width × height. That height is hard to reach with a tape; counting the siding courses between the top of the wall and the peak, times their exposure, gives it from the ground. Two gables of the same size are one triangle with a quantity of two.
| Gable | One | Two |
|---|---|---|
| 24 ft wide, 6 ft high | 72 ft² | 144 ft² |
| 30 ft wide, 8 ft high | 120 ft² | 240 ft² |
| 36 ft wide, 9 ft high | 162 ft² | 324 ft² |
Trim, gutters and openings
Behr's rule for the trim and the gutters outside is a gallon for every 8 gallons on the body: 6.29 gallons on the body is 0.79 gallons of trim paint, a gallon can, and 7.66 with the gables is 0.96 — still one. A garage door, a bay window or anything of its own size is a rectangle set to subtract; a window is taken as 15 square feet, as Behr and Sherwin-Williams do, and is a box you can change.
Primer outside
Switch "Primer" to one coat and the page adds a coat of primer over the body of the house, at 250 square feet a gallon: with the gables, 1,340 square feet is 5.36 gallons, a 5-gallon pail and a gallon can of primer beside the paint.
Prices are our own estimates, not a store's: type yours beside each can. We are not connected with any brand or store named here.