How to figure exterior paint
Exterior paint goes on the siding, not the floor plan, so start with the walls: perimeter × wall height (ground to eaves), plus the triangle of every gable end (width × peak height ÷ 2), minus doors, windows and garage doors. Then:
gallons = siding area × coats ÷ sq ft per gallon ÷ surface factor
Worked example — a two-story house on a 32×32 ft footprint: 128 ft of perimeter × 18 ft = 2,304 sq ft. Two gables, each 32 ft wide with an 8-ft peak, add 2 × 128 = 256 sq ft. Two doors (21 sq ft each) and 16 windows (15 sq ft each) remove 282 sq ft, leaving 2,278 sq ft. Two coats at 300 sq ft per gallon: 2,278 × 2 ÷ 300 = 15.2 gallons for the siding, plus about 245 sq ft of fascia and casing in the trim color.
Gallons by house size
| House | Siding | Siding + trim, 2 coats | Paint cost |
|---|---|---|---|
| 1,500 sq ft house | 1,443 sq ft | 11.1 gal | $803 |
| 2,000 sq ft house | 2,278 sq ft | 16.8 gal | $1,164 |
| 2,500 sq ft house | 2,550 sq ft | 18.8 gal | $1,298 |
| 3,000 sq ft house | 2,776 sq ft | 20.7 gal | $1,431 |
The 1,500 sq ft row is a one-story ranch; the others are two-story homes. A ranch has more wall per square foot of floor, so measure your own house.
Coverage by paint
Premium high-build exterior lines go on thicker and cover less per gallon — but often need only one coat on a same-color repaint. We plan at 300 sq ft per gallon for a typical exterior latex; pick your product in the calculator to use its own label rate.
| Paint | Label (sq ft/gal) | Coats |
|---|---|---|
| Sherwin-Williams Emerald Exterior | 250–300 | Self-priming: 2 coats new construction, 1 coat repaint |
| Sherwin-Williams Duration Exterior | 250–300 | 2 coats on bare substrates, 1 coat on repaints |
| Sherwin-Williams SuperPaint Exterior | 350–400 | 2 coats |
| Sherwin-Williams A-100 Exterior | 350–400 | 2 coats |
| Benjamin Moore Aura Exterior | 250–350 | 1–2 coats |
| Benjamin Moore Element Guard | 300–400 | 1–2 coats, self-priming |
| Behr Ultra Exterior | 250–400 | 2 coats |
| Valspar Duramax Exterior | 300–400 | 2 coats |
| Clark+Kensington Exterior Paint + Primer | 350–450 | 2 coats |
Rough siding, stucco and brick
Data-sheet rates assume smooth, sealed surfaces. Porous and rough surfaces soak up more, so the calculator plans them at a fraction of the label rate:
- Rough-sawn cedar / T1-11: 57% — Rough wood drinks paint: SW rates its deck stain at 100–200 sq ft/gal on rough wood vs 350 on smooth. We use the best case (200 ÷ 350).
- Stucco (smooth / sand): 64% — Benjamin Moore's masonry high-build rate is 160–265 sq ft/gal vs 250–350 on siding (160 ÷ 250).
- Stucco (rough / dash): 40% — SW Loxon primer covers 80 sq ft/gal on rough stucco vs 200 normally (80 ÷ 200). Spray and back-roll.
- Brick / block: 64% — Same masonry rate as smooth stucco. Painted brick can't easily go back to bare brick.
These are estimates built from maker data. Buy the last gallon or two after the first coat shows you the real spread.
Prep that changes the answer
- Bare wood, new fiber cement and fresh masonry need primer first; chalky old paint needs washing and, often, a bonding primer.
- Spraying uses more paint. Maker coverage excludes overspray, so we add 25% (our estimate) and recommend back-rolling.
- Check the minimum temperature on the can: some premium lines go down to 35°F, others need warmer weather. Stay above the dew point while it dries.
- Homes built before 1978 may have lead paint. Test before you scrape or sand.
- Dark colors on vinyl can absorb enough heat to warp it — stay at or lighter than the original color unless the line offers vinyl-safe colors.
Common mistakes
- Entering the house's floor area as the paint area. A 2,000 sq ft two-story on a 32×32 footprint has about 2,560 sq ft of gross wall.
- Forgetting the gables, which add a few hundred square feet on a typical house.
- Buying all the paint at once for rough cedar or stucco without testing the spread.
- Mixing cans mid-wall — box all the siding color in one bucket before you start.
Staining a deck or fence? Use the deck stain calculator. Painting inside? Use the room paint calculator. Re-roofing first? Try the roofing calculator.