Exterior Paint Calculator: How Much Paint for a House

Exterior paint comes in gallons and five-gallon buckets, and it adds up fast. Angi puts paint at $20 to $70 a gallon, and good exterior products sit toward the top of that range, so guessing wrong by five gallons can cost a couple of hundred dollars either way. If you can measure the house from the outside, this calculator gets you within a gallon or two.

What to measure

You need five numbers, and a 100 ft tape or a laser measure makes it a short job.

Length and width of the house at ground level. For a house with bump-outs, walk the whole outline and add every wall together, then split that total in two for length and width.
Wall height to the eaves, the bottom edge of the roof. A single-story house is usually 8 to 10 ft. Two stories are often 17 to 20 ft. You can count siding courses and multiply by their exposed height if you cannot reach.
Gables. These are the triangles of wall between the eaves and the roof peak at the ends of a house. A house with a hip roof has none.
Gable height, from the eave line up to the peak. Measure one from the ground with a laser, or estimate it from the roof pitch.
Windows and doors. Count a garage door as three regular doors.

How the math works

The calculator works it out like this:

Wall area = perimeter × wall height
Each gable = width of that end × gable height ÷ 2 (it is a triangle)
Openings: about 15 sq ft per window and 21 sq ft per door come off
Paint = paintable area × coats ÷ coverage per gallon

It then rounds up to whole gallons, because exterior paint is rarely sold in quarts, and shows how many five-gallon buckets that makes.

A worked example: a 50 x 30 ft two-story house

The house has 18 ft walls, two gables that rise 7 ft, 12 windows and 2 doors. The siding is smooth lap siding, and you want two coats.

Perimeter: 50 + 30 + 50 + 30 = 160 ft
Walls: 160 × 18 = 2,880 sq ft
Gables: 2 × (30 × 7 ÷ 2) = 210 sq ft
Openings: 12 × 15 + 2 × 21 = 222 sq ft
Paintable area: 2,880 + 210 − 222 = 2,868 sq ft
Two coats at 350 sq ft per gallon: 5,736 ÷ 350 = 16.4 gallons

Round up to 17 gallons: three five-gallon buckets and two single gallons. At $60 a gallon, that is about $1,020 of paint.

If the same house had stucco walls, coverage falls to around 250 sq ft per gallon. Two coats would then need about 23 gallons, six gallons more.

Why rough surfaces need more paint

Behr lists its masonry, stucco and brick paint at 250 to 400 sq ft per gallon, and recommends a thick-nap roller (3/4 to 1 inch) on rough surfaces. That extra nap holds more paint because the surface has more area than its flat measurements suggest. Every bump and pore of stucco, every gap between bricks has to be filled.

Rough-sawn wood, cedar shakes and split-face block behave the same way. If you are not sure which to pick, choose the rough setting. Leftover exterior paint is useful for touch-ups. Running short on the last wall, with a color match from a different batch, is the worse outcome.

One coat or two?

Two coats on the outside is the usual advice. Even Behr, which sells some exterior paints with a one-coat hide guarantee, recommends two coats on exterior surfaces for durability. The second coat is what the sun and rain wear through first, so it adds years before the next paint job.

One coat can be enough when you are refreshing the same color on siding that was painted a few years ago and is still sound. Bare wood, new stucco, a big color change or a surface you just repaired all need two coats, and often a primer first. Our primer calculator covers that.

Trim, doors and shutters

The calculator counts the body of the house: the siding or stucco. Trim is usually a different color and a glossier sheen, and it is measured by the foot, not the square foot. For most houses, 1 to 2 gallons covers fascia, window trim, corner boards and doors. Front doors and shutters often take a quart each in an accent color.

Tips before you buy

Buy from one batch. Ask the store to mix all the gallons at once, or pour them together into a bucket before you start.
Check the weather. Many exterior paints need the air and surface above 35°F, and the first 48 hours after painting matter most for drying, according to Sherwin-Williams.
Count the prep. Scraping, caulking and priming bare spots take more time than the painting itself on an older house.
Pre-1978 houses. Older exterior paint may contain lead. Scraping and sanding it is regulated work for contractors, and the EPA recommends hiring a lead-safe certified firm.

Frequently asked questions

How many gallons of paint does it take to paint a house?

Run a few typical houses through the calculator and most land between 15 and 25 gallons for two coats on smooth siding. Rough stucco or brick can push a larger house past 30 gallons.

Should I subtract windows and doors?

Yes for an exact number. If the house has many large windows, it makes a real difference. If it has only a few, some painters skip the deduction and treat it as their spare.

How much does it cost to paint the outside of a house?

Paint is the smaller part. Hiring a painter typically costs $1.50 to $4 per square foot of home. Our exterior painting cost guide has the full breakdown and an estimator.

Does a 5-gallon bucket cost less than five gallons?

Usually yes, by a few dollars per gallon, and the color is guaranteed to match all the way through.

Next step

If you are weighing a contractor against doing it yourself, run your home's size through the exterior painting cost estimator. For inside rooms, use the paint calculator.

Coverage depends on the product, the surface and the weather. Check the coverage printed on the can you buy and adjust the calculator to match.