Quantity · Exterior paint
Exterior Paint Calculator
Size exterior paint from house length, width, and wall height. Subtract doors and windows. Coverage follows substrate — wood, fiber cement, stucco, or masonry — not the interior smooth/textured table. Sheen and weather exposure guide prep; primer stays a separate line.
House footprint
Rectangular walls: 2 × (length + width) × wall height. Measure the painted wall height, not roof peak.
Openings to subtract
Doors ~21 sq ft; windows ~15 sq ft each. Count every opening you will not paint.
Prepped clapboard or smooth wood — similar to interior smooth rates.
Most common siding sheen — balance of hide and cleanability.
Stick to primer on bare or chalky surfaces plus two finish coats.
Two coats is the default for durable coverage — one coat rarely hides evenly.
Exterior paint gallons
7gal
5.66 gal raw · 2 coats · 1,062 sq ft net
Primer (separate line)
5gal
Not added into paint total — buy exterior / masonry primer as its own product.
- Wall area
- 1,224 sq ft
- Openings
- −162 sq ft
- Net area
- 1,062 sq ft
- Coverage / gal
- ~375 (350–400)
- Substrate
- Wood siding (smooth / painted)
- With waste
- 6.23 gal
- Gross = 2 × (L + W) × wall height − openings
- Paint gal = net ÷ substrate coverage × coats
- Primer = net ÷ primer coverage (1 coat, separate)
Price data updated . National US ranges from published supplier and contractor averages. Not a bid. Local quotes vary.
How exterior paint quantity is calculated
Gross wall area is 2 × (length + width) × painted wall height. Net area subtracts openings. Gallons equal net area divided by substrate coverage per gallon, times coats. Primer uses one coat at exterior primer coverage and is never added into the finish-paint total. Sheen and exposure do not replace substrate coverage — they tell you how to plan coats and prep.
wall_sq_ft = 2 × (length + width) × wall_height openings = doors × 21 + windows × 15 net_sq_ft = max(0, wall_sq_ft − openings) paint_gallons = (net / substrate_coverage) × coats × (1 + waste %) primer_gallons = (net / primer_coverage) × 1 × (1 + waste %) // separate line
Worked example. A 40 × 28 ft house with 9 ft wall height: gross 1,224 sq ft. Two doors (42) + eight windows (120) = 162 sq ft openings → 1,062 sq ft net. Smooth wood ~375 sq ft/gal, two coats → 5.66 gal raw → 7 gal with 10% waste. Primer (separate): ~3.86 gal raw → 5 gal — not included in the paint total. Stucco on the same house would need closer to 9–10 gal of finish paint.
Exterior coverage by substrate (sq ft per gallon per coat)
Unique reference for this page — weather-facing substrates, not interior drywall texture. Porous stucco and masonry cover far less per gallon than smooth wood or fiber cement.
| Substrate | Sq ft / gal / coat | Typical use |
|---|---|---|
| Wood siding (smooth) | 350–400 | Prepped clapboard / previously painted |
| Wood (weathered / rough) | 250–300 | Bare cedar, rough-sawn, chalky paint |
| Fiber cement | 300–350 | Hardie-style panels and lap |
| Stucco | 200–300 | Porous — primer critical |
| Brick / masonry | 200–250 | Block filler or masonry primer first |
- Two finish coats is the default for weather-exposed siding.
- Primer gallons are never folded into the exterior paint total.
Sheen and weather exposure
Sheen and exposure guide durability and prep. They do not replace substrate coverage in the gallon math.
| Factor | Choice | Notes |
|---|---|---|
| Sheen | Flat / matte | Hides flaws; less washable on large fields |
| Sheen | Satin / low-lustre | Most common siding sheen |
| Sheen | Semi-gloss | Trim, doors, high-wash areas |
| Exposure | Sheltered | Porch / limited sun — standard two-coat plan |
| Exposure | Full sun / weather | Primer on bare or chalky + two finish coats |
Exterior Paint calculator FAQ
- How much exterior paint do I need?
- Take net wall area (house walls minus doors and windows), divide by coverage for your substrate, then multiply by coats. Smooth wood is often 350–400 sq ft per gallon per coat; stucco and masonry can drop to 200–250. This calculator rounds up with waste and lists primer separately.
- Why does substrate matter more than sheen?
- Porosity drives how far a gallon goes. Rough wood, stucco, and brick soak paint; smooth wood and fiber cement cover farther. Sheen affects look and washability more than gallon count.
- Do I need primer on exterior siding?
- Yes on bare wood, chalky old paint, stucco, and masonry. Factory-primed fiber cement may only need spot priming — still count primer as its own product line when you buy it.
- How do I measure wall height?
- Use the painted wall height — typically foundation/siding start to eaves — not the roof peak. For two stories, use the full stacked wall height you will paint.
- Is this the same as the interior paint calculator?
- No. Interior uses smooth vs textured drywall coverage. Exterior uses substrate, sheen, and weather exposure — different table, different defaults (house footprint, more windows).
- Should trim be included?
- This tool sizes main wall fields. Trim and fascia are often a different sheen and a separate gallon — add them after you know linear feet of trim, or buy an extra gallon for cut-ins.
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