Short answer
A 2,500 sqft two-story home with a 200 ft perimeter, 18 ft wall height, 4 doors, and 18 windows has 3,246 sqft of paintable wall area. At 350 sqft per gallon over two coats, that works out to approximately 18.5 gallons of body paint—buy 20 gallons to have a comfortable buffer. You'll also need about 7 quarts of trim paint and, if priming, roughly 9.3 gallons of primer.
How this calculator works
The calculator takes six inputs and runs them through a straightforward coverage formula. Here's what each input does and why it matters.
Perimeter (ft): This is the total distance around the outside of the house measured at the foundation. A 2,500 sqft home isn't necessarily square—a rectangular footprint of 50 × 25 ft has a 150 ft perimeter, while a more spread-out 62.5 × 20 ft layout has 165 ft. For this variant, the perimeter is 200 ft, which represents a larger or more complex footprint.
Wall height (ft): Measured from finished grade to the top of the wall or the eave line—not the peak of a gable. Most single-story homes run 9–10 ft; a two-story home typically falls between 16 and 22 ft. This house uses 18 ft, a standard two-story measurement.
Gross wall area is perimeter multiplied by wall height: 200 × 18 = 3,600 sqft. That's the starting point before any deductions.
Doors and windows: Every door and window is a hole in the wall you're not painting. The calculator deducts a standard 21 sqft per exterior door (roughly a 3 × 7 ft opening) and 15 sqft per window (roughly a 3 × 5 ft opening). With 4 doors and 18 windows:
- Door deductions: 4 × 21 = 84 sqft
- Window deductions: 18 × 15 = 270 sqft
- Total deduction: 354 sqft
Net paintable area: 3,600 − 354 = 3,246 sqft
Coats: Two coats is the standard exterior repaint. The formula multiplies net area by coat count before dividing by coverage, so two coats directly doubles paint consumption. One coat on this house would require about 9.3 gallons; two coats requires 18.5 gallons.
Siding factor: This multiplier adjusts for texture. Smooth hardboard or fiber cement uses 1.0. Vinyl lap siding uses 1.1 because the shadow lines and lapped surfaces add real area. Stucco and cedar shake use 1.2 because the rough texture absorbs significantly more product. This variant uses 1.0 for smooth siding. If your house were stucco, the same geometry would require about 22.3 gallons instead of 18.5.
Coverage rate: 350 sqft per gallon. Paint cans often advertise 400 sqft/gallon. That's for ideal conditions—new, primed, smooth surfaces applied in a climate-controlled environment. Real-world exterior painting on aged siding, in varying humidity, applied by brush and roller, consistently runs closer to 350 sqft/gallon. Using 400 sqft/gallon would leave you short.
The formula in plain English:
Net paintable area × number of coats × siding factor ÷ 350 = gallons of body paint
3,246 × 2 × 1.0 ÷ 350 = 18.55 gallons
Secondary outputs:
- Total paintable wall area: 3,246 sqft — useful when getting contractor bids or buying primer.
- Trim paint quarts: 7 quarts — estimated at 1 quart per 30 linear feet of trim around the perimeter. This covers fascia boards, window casings, door casings, and corner boards at typical detail levels.
- Primer gallons (1 coat): 9.3 gallons — calculated at the same 350 sqft/gallon coverage but for only one coat. Use this if you're painting over bare substrate, major color changes, or weathered chalking paint.
Recommended materials
For a project this size, quality exterior paint makes a meaningful difference in how long you go between repaints. A premium 100% acrylic formulation holds color better and resists moisture penetration—both critical on a two-story exterior that gets full weather exposure. For application, a good airless sprayer dramatically cuts labor time on a 3,200+ sqft surface, though you'll still want to back-roll on most siding types. A 24-foot extension ladder is the minimum for safely reaching a standard 18 ft two-story wall.
- Behr Marquee exterior paint (1 gallon) — full-hide 100% acrylic, rated for 350–400 sqft/gallon, available in tintable base
- Graco Magnum X5 airless paint sprayer — handles undiluted exterior latex, suitable for full-house projects
- Werner D1224-2 24-foot aluminum extension ladder — reaches eaves on a standard 18 ft two-story wall with safe overlap
FAQ
How many gallons of paint do I need for a 2500 sqft two-story home exterior? Plan on approximately 19 gallons of body paint for two coats on a smooth-sided two-story house with a 200 ft perimeter and 18 ft wall height. That accounts for 4 doors and 18 windows subtracted from the gross wall area.
Does the 2,500 sqft floor area equal my paintable wall area? No. Floor area and paintable wall area are completely different numbers. A 2,500 sqft footprint home might have over 3,200 sqft of exterior wall surface once you account for two stories, wall height, and the actual perimeter shape.
What coverage rate does this calculator use? The calculator assumes 350 sqft per gallon, which is a conservative real-world figure for exterior paint applied with a roller or brush. Spraying can technically cover more per gallon, but you lose product to overspray, so 350 is still a reasonable planning number.
Should I buy primer separately? If you're painting over bare wood, raw stucco, or a dramatically different color, yes—plan on roughly 9.3 gallons of primer for one coat on this house. If you're recoating a sound existing paint job in a similar color, a paint-and-primer-in-one product may be sufficient.
How much trim paint do I need? The calculator estimates 7 quarts of trim paint for a 200 ft perimeter home, based on 1 quart per 30 linear feet of trim. This covers fascia, window and door casings, and corner boards at a moderate trim detail level.
What does the siding factor do? Rough or textured siding has more surface area per sqft than flat smooth siding, so it absorbs more paint. Smooth siding uses a factor of 1.0, vinyl lap uses 1.1, and stucco or cedar shake uses 1.2—meaning you'd need about 20% more paint for stucco than for smooth board siding.
Does two coats really double the paint needed? Yes, directly. The formula multiplies paintable area by the number of coats before dividing by coverage. Two coats on 3,246 sqft requires just under 19 gallons; one coat would require just under 10 gallons.
How accurate are the door and window deductions? The calculator deducts 21 sqft per door and 15 sqft per window as standard approximations. A large picture window or a wide double door will be larger than these defaults, so adjust the count or add a small buffer if your openings run big.
Should I add a waste factor on top of the calculator result? A 10% buffer is built into standard purchasing practice—round up to the next full gallon and buy one extra for touch-ups. For this house, buying 20–21 gallons instead of exactly 18.5 is prudent.
Can I use an airless sprayer and reduce my gallon count? Sprayers apply paint faster but don't reliably reduce product consumption on exteriors—overspray and the need to back-roll textured surfaces means real consumption stays close to the 350 sqft/gallon figure. Where sprayers save is labor time, not product cost.
What if my house has gables or dormers? Gables add triangular wall area that the perimeter-times-height formula doesn't capture. Measure each gable separately (base × height ÷ 2) and add that square footage to your calculated paintable area before dividing by 350.
How do I handle a house with multiple wall heights? Break the house into sections with different heights, calculate paintable area for each section separately, then add them together. Enter the combined total manually, or run the calculator multiple times and sum the gallon results.