Exterior Paint Calculator
Work out exactly how many gallons of exterior paint you need, based on your wall area, siding texture and number of coats. Add your own paint price for a full cost estimate.
How this calculator works
gallons = ceil( (wall area × coats) ÷ coverage per gallon )
Coverage per gallon changes with siding texture — a rougher surface has more actual surface area per square foot of wall and absorbs more paint, so it takes more paint to cover the same footprint compared to smooth siding.
Worked example
A 40 ft × 9 ft wall, one door subtracted, textured siding, 2 coats:
- Wall area: 40 × 9 = 360 sq ft, minus a 21 sq ft door = 339 sq ft.
- Textured siding coverage: 300 sq ft/gallon.
- Gallons: (339 × 2) ÷ 300 ≈ 2.26 → buy 3 gallons.
Coverage by siding texture
| Texture | Typical coverage |
|---|---|
| Smooth (vinyl, smooth wood) | ~350 sq ft/gal |
| Textured (lap siding, shakes) | ~300 sq ft/gal |
| Stucco / heavily textured | ~250 sq ft/gal or less |
These are general starting points — always check your specific paint product's stated coverage rate, since formulation and application method both shift the real number.
New siding vs a repaint
Bare or new siding typically needs a primer coat plus two topcoats for full, even coverage and long-term protection. A repaint over existing paint in good condition, especially in a similar color, can often get by with one topcoat, though two is still the safer choice for full opacity and an even sheen across the whole surface.
Frequently asked questions
How is exterior paint coverage different from interior paint?
Exterior surfaces are typically more textured than smooth interior drywall — lap siding, stucco, brick and rough-sawn wood all soak up more paint per square foot than a flat interior wall. Exterior coverage figures also tend to be quoted a bit more conservatively, since there's less room for a callback if a wall runs short mid-coat.
Does siding texture really change how much paint I need?
Yes, meaningfully. Smooth siding can cover 350 sq ft or more per gallon, while heavily textured siding or stucco can drop to 250 sq ft per gallon or less — a rough surface has more actual surface area per square foot of wall and absorbs more paint into its texture.
How many coats does new siding need vs a repaint?
Bare or new siding typically needs a primer coat plus two topcoats for full coverage and protection. A repaint over existing paint in good condition, especially a similar color, can often get by with one topcoat, though two is still safer for full opacity.
What are the best weather conditions for exterior painting?
Most exterior paints perform best in mild, dry conditions — avoid painting in direct hot sun, high humidity, or when rain is expected within the product's stated dry time. Check your specific paint's label for its recommended temperature range.