Short answer
A 3000 sqft modern home with a 220-ft perimeter, 20-ft walls, 4 exterior doors, and 20 windows needs approximately 23 gallons of body paint for two coats on smooth siding. The total paintable wall area is 4,016 sq ft. Add 8 quarts of trim paint and up to 11.5 gallons of primer if your siding requires it.
How this calculator works
The exterior paint calculator for a house shape takes six inputs and runs them through a straightforward area-minus-openings formula, then divides by paint coverage to give you a gallon count.
The six inputs
- Perimeter (ft): The total distance around the outside of the house at the foundation. For this 3,000 sq ft modern home, that's 220 ft. This is not the same as floor area—measure it with a tape or pull it from your blueprints.
- Wall height (ft): The average height from grade to the roofline, not the ridge peak. At 20 ft, this home is a full two stories. Single-story homes typically run 9–10 ft; two-story homes range from 18–22 ft depending on ceiling heights and floor-to-floor framing.
- Doors: Each standard exterior door is assumed to cover 21 sq ft of wall area (roughly 3 ft × 7 ft). With 4 doors, the calculator subtracts 84 sq ft from the gross wall area.
- Windows: Each window is assumed to cover 15 sq ft (approximately 3 ft × 5 ft). With 20 windows, that's another 300 sq ft removed. Combined, the openings subtract 384 sq ft.
- Coats: Two coats is the default and what most repaint jobs require. The formula multiplies the net paintable area by this number, so two coats effectively doubles your gallon count versus one coat.
- Siding factor: Smooth siding (hardiplank, smooth wood, primed surfaces) uses 1.0. Vinyl lap siding uses 1.1 because the overlap geometry adds surface area. Stucco or cedar shake uses 1.2 because the rough texture soaks up more paint per square foot. This variant uses 1.0 for a smooth modern exterior.
The formula
Net area = (perimeter × wall height) − (doors × 21) − (windows × 15)
= (220 × 20) − (4 × 21) − (20 × 15)
= 4,400 − 84 − 300
= 4,016 sq ft
Gallons = (net area × coats × siding factor) / 350
= (4,016 × 2 × 1.0) / 350
= 8,032 / 350
≈ 22.95 gallons
The denominator of 350 is the conservative coverage rate in sq ft per gallon. Most premium exterior paints list 350–400 sq ft/gal on smooth surfaces; using the lower end accounts for normal application variation and porous areas.
Secondary outputs
The calculator also produces three supporting numbers that most contractors work with:
- Total paintable wall area — 4,016 sq ft. Use this to sanity-check bids or to spec a different product.
- Trim paint — 8 quarts (1 quart per 30 linear ft of perimeter). Trim paint is typically a different sheen (semi-gloss or gloss) than body paint. This estimate covers fascia, corner boards, and window/door casing at typical proportions.
- Primer gallons — 11.5 gallons for one primer coat. This uses the same net area but only one coat and no siding factor. Primer is needed on bare wood, bare fiber cement, any area where you've scraped to bare substrate, or any color change from very dark to very light.
What the output represents
The 23-gallon figure is paint-in-the-can before any waste factor. Brushing and rolling waste is typically 5–10%; spray application adds another 10–15% for overspray. Round up to the next whole gallon when purchasing, and plan for at least a 10% overage—roughly 2–3 extra gallons for this project—to cover touch-ups, partial wall sections, and the inevitable second-coat variation that shows up once the first coat dries.
Recommended materials
For a project requiring 23 gallons of body paint on a modern home, product quality matters more than on interior work—exterior paint faces UV, moisture, and temperature swings year-round. A high-solids 100% acrylic latex formula will outperform budget options in both coverage and durability. An airless sprayer pays for itself quickly on a job this size, and having a solid 24-ft extension ladder is non-negotiable for reaching 20-ft walls safely.
- Behr Marquee exterior paint (1 gallon) — a high-hide, one-coat capable formula with solid UV resistance; buy in 5-gallon buckets once you've confirmed your color.
- Graco Magnum X5 airless paint sprayer — handles up to 125 gallons per year and can spray unthinned exterior latex; good fit for a single-home project at this scale.
- Werner D1224-2 24-foot aluminum extension ladder — reaches eave height on a 20-ft wall with safe overlap on both ends; aluminum keeps it manageable at the top of that reach.
FAQ
How many gallons of exterior paint does a 3000 sqft modern home need? Using a 220-ft perimeter, 20-ft wall height, 4 doors, and 20 windows with 2 coats, the calculator returns approximately 23 gallons of body paint. That covers roughly 4,016 sq ft of paintable wall surface at 350 sq ft per gallon.
Does the 23-gallon figure include primer? No. Primer is calculated separately. One primer coat for this home requires about 11.5 gallons. Budget for that in addition to your 23 gallons of body paint if you're painting bare or heavily weathered siding.
How much trim paint do I need? The calculator estimates 1 quart of trim paint per 30 linear feet of trim. With a 220-ft perimeter, that comes to 8 quarts (2 gallons) of trim paint. Adjust up if your home has heavy window casing, corner boards, or wide fascia.
What does the siding factor do? Rough or textured surfaces absorb more paint than smooth ones. Smooth siding uses a factor of 1.0. Vinyl lap uses 1.1, and stucco or cedar shake uses 1.2, which can push your total to 27–28 gallons on the same house.
Why does the formula deduct for doors and windows? Each standard exterior door subtracts 21 sq ft from the paintable area, and each window subtracts 15 sq ft. On a home with 4 doors and 20 windows, that removes 384 sq ft—about one gallon of paint.
Is 350 sq ft per gallon a reliable coverage rate? Most quality exterior paints list 350–400 sq ft per gallon on smooth surfaces. The calculator uses 350 as a conservative figure. Check your specific product's label; some thicker formulas cover less.
Should I round up when buying paint? Buy in whole gallons. Round 22.9 up to 23, then add 10% for waste, touch-ups, and second-coat variation. That puts your purchase quantity at 25–26 gallons for a job this size.
Can I use a paint sprayer for exterior work on a home this size? Yes, and it's often faster than rolling for a large modern home with flat facades. You'll need to mask all windows, doors, trim, and adjacent surfaces thoroughly. Expect 15–20% more paint consumption with a sprayer compared to rolling.
How does wall height affect paint quantity more than square footage? Square footage is a floor area measurement that doesn't directly translate to wall area. A two-story modern home with 20-ft walls will have significantly more paintable surface than a single-story ranch at the same floor footprint.
What if my home has gable ends? Gable triangles add wall area the perimeter-times-height formula doesn't capture. Measure each gable's base and height, calculate the triangle area (base × height ÷ 2), and add those square footages before dividing by 350.
How many coats does exterior paint typically need? Two coats are standard for a repaint over existing sound paint. Going from a dark color to a light one, or painting bare wood or fresh stucco, may require three coats or a dedicated primer coat first.
Does paint brand affect the gallon count? Coverage per gallon varies by formulation. The calculator's 350 sq ft/gallon is a safe baseline for most premium exterior paints. Always check the coverage on the product data sheet and use that number if it differs.