Paint calculators
Exterior Paint Calculator
Exterior paint is the most expensive paint you will buy — premium exterior gallons run $55–85 in 2026 — and running short means a second trip while scaffolding sits in your yard. Worse, exterior color matching between batches is unforgiving in daylight.
This calculator estimates whole-house exterior paint from your home's footprint: width, depth, wall height, and stories give the gross wall area, then windows and doors are subtracted using standard allowances. The key difference from interior math is the siding adjustment — brick drinks far more paint than smooth siding — so pick your siding type and the coverage rate adjusts automatically.
- Paintable wall area
- 1020 sq ft
- Exterior paint needed
- 6 gallons6.00 gal · 2 coats at ~350 sq ft/gal (smooth siding, estimate)
How we calculate this (with your numbers)
Perimeter = 2 × (40 + 30) = 140 ft; gross wall = 140 × 9 ft × 1 story = 1260 sq ft
Minus 12 windows × 15 and 3 doors × 20 = 1020 sq ft paintable
Paint = 1020 × 2 coats ÷ ~350 sq ft/gal = 5.83 gal → 6 gallons (rounded up to the nearest quart)
Siding coverage rates are estimates: smooth ~350, textured/stucco ~300, brick/masonry ~250 sq ft/gal.
How the math works
Worked example
A single-story 40 × 30 ft house, 9 ft walls, 12 windows, 3 doors, smooth siding, 2 coats:
- Perimeter = 2 × (40 + 30) = 140 ft
- Gross wall = 140 × 9 = 1,260 sq ft
- Minus openings: 1,260 − (12 × 15) − (3 × 20) = 1,020 sq ft paintable
- Paint = 1,020 × 2 ÷ 350 = 5.83 gallons
- Rounded up: 6 gallons (5 gal + 4 qt)
Limitations
Frequently asked questions
It depends on the footprint and siding, not just floor space. A single-story 50×40 ft house (2,000 sq ft footprint) with 9 ft walls has about 1,335 paintable square feet after windows and doors — roughly 8 gallons for two coats on smooth siding. See our worked guide for the full breakdown.
Yes, significantly. Smooth siding runs about 350 sq ft per gallon, textured or stucco about 300, and brick or masonry about 250 — these are estimates, since porous surfaces absorb more paint. This calculator adjusts coverage automatically when you pick a siding type.
Two coats is the standard for exterior work — UV, rain, and temperature swings punish thin paint jobs. One coat is only realistic for a same-color refresh on paint that is still in good condition.
This calculator does not add gable triangles automatically. If your house has prominent gables, add roughly 10–15% to the result (estimate) or measure each triangle as base × height ÷ 2 and add it to your wall area.
On bare wood, raw stucco, or chalky old paint — yes. On previously painted siding in sound condition, a quality exterior paint (many are self-priming for repaints) is usually enough. Spot-prime any bare patches regardless.
Related calculators & guides
- Interior paint calculator — the same math for inside walls
- Paint cost calculator — budget the whole exterior job including supplies
- Primer calculator — for bare wood and raw masonry
- How much exterior paint for a 2,000 sq ft house — full worked example with siding variants