Exterior Paint Calculator
To estimate exterior paint, find the wall area (perimeter × total height), subtract about 21 sq ft per door and window, multiply by the number of coats, and divide by 300 sq ft per gallon. A typical 40×30 ft two-story home needs about 14 gallons for two coats.
- Coverage per gallon
- ~300 ft²
- Standard coats
- 2
- Repaint every
- 7–10 yrs
Your measurements
All stories combined (e.g. 18 ft for 2 stories).
Each opening subtracts ~21 sq ft of wall.
Enter your measurements
Fill in the fields to see your estimate.
The formula
Gallons = (Wall area − openings) × coats ÷ 300 sq ft per gallonHow to calculate it manually
- 1
Measure the perimeter
Add all exterior wall lengths — 2 × (length + width) for a rectangular home.
- 2
Multiply by total height
Use the full height of all stories (e.g. ~18 ft for two stories).
- 3
Subtract openings
Remove about 21 sq ft for each door and window.
- 4
Divide by coverage
Exterior paint covers ~300 sq ft per gallon per coat — less on rough surfaces.
Example calculation
A 40×30 ft two-story home: perimeter 140 ft × 18 = 2,520 ft² − 168 (8 openings) = 2,352 ft² × 2 coats = 4,704 ÷ 300 ≈ 15.7 gallons.
Exterior paint needed by home size
Gallons for two coats, minus openings. Rough surfaces (stucco, brick) need more.
| Home size | Approx. wall area | Gallons (2 coats) |
|---|---|---|
| 1-story 1,200 ft² | ~1,100 ft² | ~7–8 gal |
| 2-story 1,800 ft² | ~2,300 ft² | ~14–16 gal |
| 2-story 2,500 ft² | ~2,900 ft² | ~18–20 gal |
Common exterior paint estimating mistakes
Skipping primer and prep
Bare wood, repairs, and big color changes need primer. Power-wash and scrape first or the paint won't last.
Underestimating rough surfaces
Stucco, brick, and rough wood drink paint — expect 20–40% less coverage than smooth siding.
Buying for one coat
Exterior work almost always needs two coats for even color and weather protection.
Forgetting trim and doors
Trim, fascia, and doors often use a different paint — budget for those separately.
Frequently asked questions
Related guides
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Ready to start your painting project?
Run the numbers above, then explore related tools and guides to plan every step.