Exterior paint calculator

How this calculator works

It measures the walls as one strip around the house, adds the triangular gable ends, and subtracts doors (21 sq ft), windows (15 sq ft) and two-car garage doors (112 sq ft). It multiplies by coats, divides by coverage, adds waste and rounds up to buckets, gallons and quarts.

The default coverage is 300 sq ft per gallon, the conservative end of the 250–400 sq ft exterior paints list for smooth siding. Rough surfaces such as stucco, split shakes and brick can drop to 150–250, so check the can. Trim is estimated as boards about 6″ wide around every opening, at the corners and along the eaves.

Worked example

A 40′ × 30′ house with 10′ walls has 2 × 70 × 10 = 1,400 sq ft of wall, and two 6′ gables add 180 sq ft. Take off two doors (42), twelve windows (180) and a garage door (112) and 1,246 sq ft is left. Two coats at 300 sq ft per gallon is 8.31 gallons; with 10% waste that is 9.14 gallons, which the list buys as one 5-gallon bucket, 4 gallons and 1 quart. The 436 ft of trim needs 1.60 gallons, so 2 gallons of trim paint.

Tips before you buy

• Measure wall height from the ground (or top of the foundation) to the underside of the eaves, not to the roof line.
• Wash the siding and let it dry for a day or two before painting; paint does not bond to chalk, dirt or mildew.
• Paint in the shade and avoid days below the temperature on the can or with rain due before the paint cures.
• Bare wood, new siding and patched areas need an exterior primer first. Work that out with the primer calculator.
• Box all the cans together in one bucket so every wall gets the same color.

Questions

How many square feet does a gallon of exterior paint cover?

Most exterior paints list 250 to 400 square feet per gallon on smooth, sound siding. Rough-sawn wood, shakes and stucco absorb much more, often 150 to 250 sq ft per gallon, so set the coverage from the can for your surface.

How many coats does a house need?

Two coats give the best color and durability, especially for a color change or weathered siding. One coat can work when you repaint the same color over paint that is still in good condition.

How do I measure a gable end?

Measure the house width at the gable wall and the height from the eaves line to the peak. The triangle is half of width times height, which is what the calculator adds for each gable.

Is a 5-gallon bucket worth it?

For a whole house, yes. A bucket keeps the color consistent across walls and usually costs less per gallon than five single cans. The list switches to buckets automatically once you need five gallons or more.