Short answer
A 1,800 sqft Cape Cod house with a 170-ft perimeter, 16-ft walls, 3 doors, and 12 windows needs about 14.2 gallons of body paint for two coats—round up to 15 gallons at the store. You'll also want 6 quarts of trim paint and, if priming, approximately 7 gallons of primer.
How this calculator works
The calculator starts with gross wall area and works down to a gallon count through a series of subtractions and multipliers.
Step 1 — Gross wall area
Multiply the house perimeter by the wall height: 170 ft × 16 ft = 2,720 sqft of gross wall surface.
Step 2 — Subtract openings
Doors and windows don't get painted, so they're removed from the total. The formula uses standard rough-opening estimates: 21 sqft per door and 15 sqft per window.
- 3 doors × 21 sqft = 63 sqft
- 12 windows × 15 sqft = 180 sqft
- Total deductions: 243 sqft
2,720 − 243 = 2,477 sqft of paintable wall area
That 2,477 sqft figure is also shown as a secondary output so you can sanity-check it against your own field measurements.
Step 3 — Apply the siding factor
Textured or profiled siding has more physical surface area than a flat plane of the same dimensions. A smooth surface (HardiePlank, smooth stucco, painted wood) stays at 1.0. Standard vinyl lap siding uses 1.1. Cedar shake or rough stucco uses 1.2. For this variant the siding factor is 1.0, so the area stays at 2,477 sqft.
Step 4 — Multiply by coats
Two coats means you're covering that area twice: 2,477 × 2 = 4,954 sqft total paint coverage needed
Step 5 — Divide by coverage rate
Most exterior paints state 400 sqft/gallon on the label under ideal conditions. The calculator uses 350 sqft/gallon, which is the real-world rate once you account for uneven surfaces, end-grain absorption on wood, and the fact that painters don't squeegee every drop out of the roller.
4,954 ÷ 350 = 14.15 gallons → buy 15
Secondary outputs explained
Trim paint (6 quarts): The formula uses 1 quart per 30 linear feet of trim—a rule of thumb based on the narrow width of fascia, corner boards, window casings, and door surrounds. At 170 ft of perimeter, that's 6 quarts. Buy trim paint in a different sheen (semi-gloss or gloss) than the body color.
Primer (7 gallons): Calculated as one coat at 350 sqft/gallon over the 2,477-sqft paintable area. You only need primer if you're painting raw or bare wood, switching from dark to light, or the existing finish is chalking, peeling, or heavily stained. For a same-color refresh over solid, adhered paint, skip primer and put the budget toward a quality body paint.
About the perimeter input
The calculator needs the full exterior perimeter, not square footage. Measure each exterior wall with a tape measure and add them up. For a simple rectangular 1,800 sqft Cape Cod footprint, 42 ft × 28 ft yields 140 ft of perimeter. A more complex plan with bump-outs, attached garage, or irregular shape pushes that number higher—this variant uses 170 ft to reflect a typical Cape with an attached garage wing.
What the output doesn't cover
The formula calculates vertical wall surface only. Soffits, fascia, porch ceilings, and gable-end triangles above the main eave line are not included. Cape Cods often have prominent gable ends—measure those triangles (½ × base × height) and add the area to your total before finalizing your paint order.
Recommended materials
For a 15-gallon exterior repaint, you want a self-priming acrylic latex with high hide and a 15-year-plus finish warranty—it reduces the chance you need a third coat and holds up to Cape Cod's seasonal temperature swings. An airless sprayer cuts application time significantly on a two-story structure with dormers, but rolling and back-brushing on wood siding gives better adhesion. A 24-foot extension ladder handles most of the eave work on a 1.5-story Cape; for the peak of steep gables you may need scaffolding.
- Behr Marquee exterior paint (1 gallon)
- Graco Magnum X5 airless paint sprayer
- Werner D1224-2 24-foot aluminum extension ladder
FAQ
How many gallons of paint do I need for a 1,800 sqft Cape Cod house? The calculator outputs roughly 14.2 gallons for two coats of body paint, so buy 15 gallons to have a small buffer. That figure assumes a 170-ft perimeter, 16-ft wall height, 3 doors, and 12 windows with smooth siding.
What does "paintable wall area" mean and why does it matter? Paintable wall area is gross wall square footage minus the space taken by doors and windows. Paint doesn't stick to glass or metal, so subtracting those openings gives you the surface that actually absorbs paint.
How much trim paint does a Cape Cod need? The secondary output estimates 6 quarts for a 170-ft perimeter, using a rule of 1 quart per 30 linear feet of trim. Trim paint is usually a different sheen—semi-gloss or gloss—so budget it separately from your body color.
Do I need primer before repainting? Not always. If the existing paint is sound, clean, and the same sheen, you can skip primer and add a third body coat instead. If you're changing from dark to light, painting raw wood, or the old paint is chalking, plan on 7 gallons of primer for one coat.
What is the siding factor and when should I increase it? The siding factor accounts for extra surface area that rough or textured siding presents. Smooth HardiePlank or wood stays at 1.0; standard vinyl siding uses 1.1; stucco or cedar shake uses 1.2, adding 10–20% more paint to the estimate.
Should I spray or roll exterior paint on a Cape Cod? Spraying is faster and gives better coverage on complex trim details and dormers typical of Cape Cods, but you need to mask every window, door, and foundation. Rolling and back-brushing immediately after spraying ("spray and back-roll") gives the best adhesion on wood and fiber cement.
How long does a gallon of exterior paint cover? Most exterior paints cover 350–400 sqft per gallon on smooth surfaces. This calculator uses 350 sqft/gallon, which is the conservative end to account for slight texture and absorption variation.
Can I split paint purchases between stores if I need multiple gallons? Only if they're from the same dye lot. Color-matched paint can vary batch to batch, and the difference becomes visible once it cures. Buy all your gallons in one order, or at minimum have them all tinted from the same base batch at the same location.
Does the calculator include the roof or soffit areas? No. The formula covers vertical wall surfaces only. Soffits, fascia, and gable ends that extend above the main wall line require a separate measurement. Gable triangles on a Cape Cod can add 100–200 sqft depending on pitch.
How does wall height work on a Cape Cod, which has a steep roof and shed dormers? Use the average wall height from foundation to eave—typically 14–18 ft on a 1.5-story Cape. The sloped portion above the eave on gable ends should be calculated separately as a triangle and added to your total.
What's the difference between one coat and two coats in the estimate? Two coats doubles the paint required. The calculator's default is 2 coats, which is standard for full repaints and color changes. One coat may be acceptable for a same-color refresh over sound, lightly faded paint.
How far in advance should I buy paint before starting? Buy it at least a few days before you start so you can verify all cans are the same dye lot and inspect for any mixing errors in daylight. Exterior paint stores well sealed, so there's no downside to purchasing early.