Exterior paint calculator
The 40 x 30 one-story the form opens on takes 7 gallons of body color for two coats: 1,210 sq ft of smooth siding once two doors and ten windows come out, at 350 sq ft per gallon. Put the same house in stucco and it wants 10 gallons. That gap is the miss that sends people back to the store on a Sunday.
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How the math works
Paintable area is the house perimeter times the painted wall height, minus openings. We figure 10 ft of height per story: 9 ft of wall plus the rim and eave band that gets painted with it. A 40 x 30 one-story is a 140 ft perimeter times 10 ft, so 1,400 sq ft of wall; take out two doors (20 sq ft each) and ten windows (15 each) and you're painting about 1,210 sq ft. Two coats on smooth siding at 350 sq ft per gallon is 6.9 gallons. Buy seven.
Then the surface has its say. The same 1,210 sq ft in stucco covers at 250 sq ft per gallon and wants 10 gallons. This is the single biggest miss in exterior estimates, bigger than any measuring error: people buy for the can's smooth-wall number and paint a wall that drinks.
Questions people ask
How much paint does a 1,500 sq ft house exterior take?
A one-story house around 40 x 30 ft runs about 1,200 sq ft of paintable siding after doors and windows, which is 7 gallons for two coats on smooth siding. Stucco or brick on the same footprint pushes it to 10, because rough surfaces cover at 250 sq ft per gallon instead of 350.
Why does the surface matter so much outside?
Porosity and texture. Previously painted smooth siding covers near the 350 the can promises. Rough-sawn wood and fiber cement land around 300. Stucco, brick, and split-face block soak paint into every pore and drop real coverage to 250 or worse. Same house, three gallons apart.
Do I count the gable ends?
Yes if they are sided and getting painted. Our story heights build in some allowance (10 ft per story covers the rim and eave bands), but a tall gable adds real area: width times height divided by 2 per gable. Add it to your measurements or bump the result by a quart or two.
One coat or two on an exterior?
Two for a color change or chalky, weathered paint; one can be enough when you are refreshing the same color on sound, cleaned siding. Most repaints are two. Primer is a separate question: bare wood, tannin-bleeding cedar, and chalky surfaces want a primer coat first.
By house size
The calculator above takes a footprint and a story count, so it prices a 1,500, 2,000, 2,500 or 3,000 sq ft house on any of the three siding surfaces without a separate page per size. Interior walls of the same house: how much paint for a 2,000 sq ft house. Surface rates: coverage per gallon.
Exterior wood that takes stain, not siding paint: the deck stain calculator and the fence stain calculator use their own coverage rates.