The short answer
A 40 × 30 ft one-story house with two 30 ft wide, 8 ft rise gables, 2 doors and 10 windows has 1,450 sq ft to paint. Two coats of smooth siding at 350 sq ft per gallon need 8.29 gallons: 1 five-gallon bucket + 3 gallons + 2 quarts, about $375.
Worked example
| Step | Math | Result |
|---|---|---|
| Walls | (2 × (40 + 30)) × 10 ft | 1,400 sq ft |
| Gables | 2 × ½ × 30 × 8 | + 240 sq ft |
| Openings | 2 doors × 20 + 10 windows × 15 | − 190 sq ft |
| Paintable | 1,400 + 240 − 190 | 1,450 sq ft |
| Gallons (2 coats) | 1,450 × 2 ÷ 350 | 8.29 gal |
Siding coverage presets
- Smooth siding: 350 sq ft per gallon
- Wood clapboard: 300
- Rough cedar: 250
- Stucco or brick: 200
These are planning starting points: rough, porous surfaces soak up more paint, and PaintCare notes rough textures can need up to 50 percent more. Check your can’s label.
We use 10 ft per story as a simple rule. For tall first floors or a raised foundation, type a custom wall height.
FAQ
How much paint do I need to paint a house exterior?
Find the wall area (perimeter × height), add gables, subtract doors and windows, multiply by coats and divide by coverage. A 40 × 30 ft one-story house with gables is about 1,450 sq ft, or 8.3 gallons for two coats.
How do I figure gables?
Each gable is a triangle: ½ × width × rise. Add it to the wall area.
Is it cheaper to buy 5-gallon buckets?
At the default prices a bucket ($200) costs the same as four gallons plus a quart ($180 + $20) and holds a full 5 gallons, so past 4 gallons the bucket wins. The calculator picks the cheapest mix for you.
Do I need primer outside?
Bare wood, patched areas and big color changes usually do. Toggle primer to add it.