Paint Calculator
A paint calculator estimates the number of paint gallons required for interior and exterior painting projects based on wall dimensions, doors, and coats. Factoring in the standard coverage of 350 to 400 square feet per gallon, it prevents overbuying by estimating exact paint volumes needed.
By Sofia Marchetti (Home & Wellness Reviewer) · Reviewed by Daniel OkoroUpdated · Published
Wall Area: 0 sq ft (2 coats)
How Does the Paint Calculator Work?
- Enter room length, width, and ceiling height.
- Specify number of standard doors (20 sq ft each) and windows (15 sq ft each).
- Select 1 coat or 2 coats of paint to get exact gallons to purchase.
What Is the Paint Formula?
Standard interior paint covers approximately 350 to 400 square feet per gallon.
How Do You Calculate Paint Step by Step?
Painting a 12×15 ft room with 8 ft ceilings, 1 door, 2 windows, and 2 coats of paintGross wall perimeter: 2 × (15 + 12) = 54 ft. Gross area: 54 × 8 = 432 sq ft
Deductions: 1 door (20 sq ft) + 2 windows (30 sq ft) = 50 sq ft
Net wall area per coat: 432 - 50 = 382 sq ft
Total painted area (2 coats): 382 × 2 = 764 sq ft
Gallons needed: 764 ÷ 350 = 2.18 gallons (buy 3 gallons)
Typical interior paint coverage per US gallon
| Surface | Coverage per gallon (one coat) |
|---|---|
| Smooth primed drywall | 350 - 400 sq ft |
| Textured or porous walls | 250 - 350 sq ft |
| Ceilings | 300 - 350 sq ft |