Exterior Paint Calculator
Calculate how many gallons of exterior paint you need for any house size. Enter perimeter, height, coats, doors, and windows.
How to Use This Calculator
To calculate exterior paint, enter your house perimeter as the length and 1 as the width — this effectively enters total linear feet. Then set the wall height from ground to eaves (not roof peak). For a typical single-story house, that's 8 to 10 feet. For two-story, measure the full height to the eaves, usually 16 to 20 feet.
Alternatively, enter length and width of the building footprint. The calculator computes 2 × (length + width) × height automatically, which equals the full exterior wall perimeter. Either approach gives the same result.
Enter your doors and windows to subtract those unpainted surfaces. Set coats to 2 for a standard re-paint. Use 3 for bare or heavily weathered siding. After getting your gallon result, add 15–20% more gallons if painting rough stucco, textured siding, or raw wood, since exterior paint covers 250–300 sq ft per gallon on rough surfaces versus the 350 sq ft used in the calculation.
How to Calculate Exterior Paint
The formula is the same as interior painting: wall area = 2 × (length + width) × height. Subtract openings: doors at 21 sq ft each, windows at 15 sq ft each. Then apply coverage and waste.
Formula: gallons = ⌈(paintable area × coats × 1.1) ÷ coverage⌉
Example: house 40 ft long, 30 ft wide, 9 ft wall height, 2 coats, 3 doors, 8 windows. Wall area = 2 × (40 + 30) × 9 = 1,260 sq ft. Subtract: 3 × 21 + 8 × 15 = 63 + 120 = 183. Paintable area = 1,077 sq ft. Using 300 sq ft/gal for rough siding: ⌈1,077 × 2 × 1.1 ÷ 300⌉ = ⌈7.90⌉ = 8 gallons.
The calculator uses 350 sq ft/gal as its baseline. For smooth fiber cement or previously painted siding, this is accurate. For rough wood, stucco, or masonry, divide your calculator result by 350 and multiply by 300 to get the adjusted count — or simply add 2 gallons per 10 gallons the calculator returns as a quick field adjustment.
Exterior Painting Tips
Never paint in direct sunlight or when surface temperatures exceed 90°F. Hot surfaces cause paint to dry too fast, leaving lap marks and reducing penetration. Start on the shaded side of the house in the morning and follow the shade around the building. Stop painting by mid-afternoon on hot days and resume in the evening when temperatures drop.
Wash the surface before painting. Exterior walls accumulate mildew, chalk, and airborne grease — especially near kitchens and garages. A pressure washer at 1,200–2,500 PSI and a TSP substitute solution removes all of it. Paint applied over mildew will peel within two years regardless of brand or quality. Wait until the surface is completely dry before priming or painting.
Caulk all gaps before painting, not after. Gaps around windows, door frames, trim, and siding joints admit water that causes paint failure from behind. Use a paintable exterior caulk, fill every gap over 1/16 inch, and allow it to fully cure before painting over it. Skipping this step is the single most common cause of exterior paint failing within three years.
What to Buy
For wood siding: Sherwin-Williams Emerald Exterior or Benjamin Moore Aura Exterior in satin finish. Both carry a lifetime limited warranty and resist cracking and peeling in freeze-thaw climates. Expect 350 sq ft per gallon on smooth painted surfaces, 250–300 on rough or bare wood.
For stucco and masonry: use a masonry-specific exterior paint or elastomeric coating. Elastomeric paint bridges hairline cracks and prevents water intrusion. Coverage is lower — 100–150 sq ft per gallon for heavy-bodied elastomeric coatings. Double the calculator's gallon count if using elastomeric on textured stucco.
For primer: KILZ Premium Exterior or Zinsser Bulls Eye 1-2-3 Exterior on most surfaces. Use Zinsser B-I-N shellac-based primer specifically for cedar and redwood to block tannin bleed. Buy 1 gallon of primer per 2 gallons of finish coat — primer covers the same area as finish paint and a single coat is usually enough.
Frequently Asked Questions
How many gallons of exterior paint do I need for a 2,000 sq ft house? +
A 2,000 sq ft house with a standard 8-foot wall height has roughly 1,600 sq ft of exterior wall area per floor (perimeter × height). A single-story house with a 50 × 20 ft footprint has a perimeter of 140 ft × 8 ft = 1,120 sq ft, minus doors and windows. Exterior paint covers about 300 sq ft per gallon on average siding. For 1,000 sq ft paintable area, 2 coats, and 10% waste: ⌈1,000 × 2 × 1.1 ÷ 300⌉ = 8 gallons. Enter your actual perimeter × height in the calculator for an exact count.
Does exterior paint cover more or less area than interior paint? +
Exterior paint covers less per gallon on most surfaces. Interior walls are smooth and previously painted, yielding 350–400 sq ft per gallon. Exterior surfaces — rough wood siding, stucco, fiber cement, concrete block — absorb more, typically 250–350 sq ft per gallon. Rough-sawn or unpainted wood can drop as low as 200 sq ft per gallon on the first coat. Add 15–20% to your calculator result when painting textured or weathered surfaces.
How do I measure my house for exterior paint? +
Measure the perimeter of the house (add all four wall lengths together). Multiply by the wall height from ground to eaves — not roof peak. That gives gross wall area. Subtract each door at 21 sq ft and each window at 15 sq ft. For a two-story house, multiply by the total height to the eaves. For gable ends, calculate each triangle separately: area = (base × height) ÷ 2.
How many coats of exterior paint do I need? +
Two coats is standard for most exterior re-paints over an existing same-color surface. Use three coats when making a dramatic color change, painting bare wood or siding for the first time, or painting over surfaces with heavy chalking or weathering. Priming bare wood or repair patches before top coats significantly improves adhesion and can reduce your finish coat count from three to two.
What is the best exterior paint for wood siding? +
Acrylic latex is the standard choice for wood siding in most climates. It stays flexible as wood expands and contracts with humidity changes, resists cracking, and cleans up with water. Benjamin Moore Aura Exterior and Sherwin-Williams Emerald Exterior are the benchmark products. For raw or bare wood, use an oil-based primer first — it penetrates deeper than latex primer and prevents tannin bleed-through on cedar and redwood.
Can I use a sprayer instead of a roller for exterior paint? +
Yes, and a sprayer is significantly faster on large exterior surfaces. Back-rolling — spraying and then immediately rolling through the wet paint — is best practice because it forces paint into gaps and textures that spray alone can miss. Expect 30–40% more paint consumption with a sprayer due to overspray. Add that buffer to your calculator result if spraying without back-rolling. Mask windows, trim, and landscaping thoroughly before spraying.
How long does exterior paint last? +
Quality exterior paint on properly prepared surfaces lasts 7–15 years depending on climate, sun exposure, and paint quality. South-facing walls degrade faster due to UV exposure. Signs it's time to repaint: widespread chalking (white powder when you rub the surface), peeling or bubbling, fading beyond touch-up level, or visible bare wood. Proper prep — cleaning, sanding, priming bare areas — is more important than paint brand for longevity.
Do I need primer for exterior painting? +
Primer is essential for: bare wood or bare siding, any surface with more than 25% of the old paint removed, repaired areas, cedar or redwood (to prevent tannin bleed), and when making a drastic color change. Primer is not necessary when repainting over a sound existing coat of the same color. Self-priming exterior paints exist but perform better as a second coat, not as a substitute for a dedicated primer on bare surfaces.
