Exterior Paint Calculator

How much paint one gallon covers

Exterior paint coverage is quoted as a range, not a single number. A gallon covers 250 to 400 square feet in one coat, according to Behr's exterior paint guide. Where you land in that range depends on the surface.

• 400 square feet per gallon: smooth, previously painted siding in a similar color
• 350 square feet per gallon: typical wood or vinyl siding, a safe default
• 250 square feet per gallon: rough, porous, textured or bare wood, or a dramatic color change

Stucco, brick and rough sawn wood soak up more paint than smooth siding, so use the low end of the range for those. If you are changing from dark to light or the other way around, budget for an extra coat or a tinted primer. The calculator above defaults to 350 square feet per gallon and lets you change it.

Worked example: a 1,600 square foot single story house

Measure the perimeter of the house and the height of the walls from the foundation to the roofline, excluding the gables. Say the perimeter is 160 feet and the walls are 9 feet tall.

• Wall area: 160 ft x 9 ft = 1,440 square feet
• Windows: 12 windows x 15 square feet = 180 square feet
• Doors: 3 doors x 20 square feet = 60 square feet
• Net area to paint: 1,440 - 180 - 60 = 1,200 square feet
• Two coats: 1,200 x 2 = 2,400 square feet
• Paint needed: 2,400 / 350 = 6.9, so buy 7 gallons

Now add the trim and gutters, which are usually a different color and a different can. Trim runs about 200 linear feet at a 6 inch width, so that is 100 square feet. Two coats is 200 square feet, about 1 gallon. Gutters run 120 linear feet, which counts as roughly 120 square feet, and two coats is 240 square feet, so another gallon. The total order is 7 plus 1 plus 1, or 9 gallons.

At $45 a gallon that is about $405 in paint, before brushes, tape and primer. Buying one extra gallon up front is cheaper than a second trip in the middle of a job, and most stores accept unopened cans for return.

Worked example: a two story house

A two story house with a 140 foot perimeter and 18 feet of wall height:

• Wall area: 140 ft x 18 ft = 2,520 square feet
• Two gable ends at 30 feet wide and 8 feet tall: 2 x (30 x 8 / 2) = 240 square feet
• Gross area: 2,520 + 240 = 2,760 square feet
• Windows: 20 x 15 = 300 square feet, doors: 4 x 20 = 80 square feet
• Net area: 2,760 - 300 - 80 = 2,380 square feet
• Two coats: 4,760 / 350 = 13.6, so buy 14 gallons

Two story houses cost more than the extra square footage suggests, because ladders and scaffolding take time and tall walls are harder to keep wet at the lap line. If you are hiring out, most painters quote labor by the square foot of wall area, and the paint is often the smaller line on the estimate.

Paint coverage at a glance

Gallons to buy, rounded up, at a 350 square foot coverage rate unless noted. This assumes you subtract doors and windows first.

Two coats is the standard for exterior work, not one. Sun, rain and temperature swings break down a single coat faster, and a thin coat lets the old color show through on a color change. If the existing paint is in good shape and you are matching the color, one coat can work, but the second coat is what buys you the years.

Trim, doors and gutters add up

The body of the house is the easy part to estimate. The trim is where people run short, because it is slow to paint and the area is easy to forget. A simple rule from the paint guides is one gallon of trim paint for every eight gallons of body paint, but that breaks down on houses with a lot of detail.

• Trim: measure the total linear feet and multiply by the width in feet. A 6 inch trim board is 0.5 feet wide, so 200 linear feet is 100 square feet.
• Doors: about 20 square feet each, counting both sides if you paint both. Front doors often take a separate color and a separate quart.
• Gutters and downspouts: one linear foot of gutter counts as about one square foot. A 120 foot run is 120 square feet.
• Fascia and soffits: add these to the trim total if they get painted with the trim color.

Trim paint usually comes in quarts and gallons only, so rounding up is normal. A quart covers about 100 square feet in one coat, which handles most front door and shutter jobs with some left over.

Before you paint: lead paint and surface prep

If the house was built before 1978, assume the existing paint may contain lead. Any scraping, sanding or power washing that disturbs old paint can create lead dust, and that dust is a health risk, especially for children. The EPA's lead safe renovation guide for DIYers covers how to test, contain the work area and clean up. A simple lead test kit costs a few dollars and settles the question in minutes.

Surface prep decides how the paint job ages. Wash off dirt and chalk, scrape loose paint, sand the edges smooth, and prime any bare wood or patched spots. Caulk gaps around trim and windows so water cannot get behind the paint. Paint over a wet surface or in direct sun and the film will fail early, no matter how good the paint is.

Finally, check the weather. Most exterior paints want temperatures above 50°F and a dry surface, with rain out of the forecast for at least 24 hours after application. Painting in the shade of the house as the sun moves keeps the paint from drying too fast at the lap line.