Paint Calculator
Calculate exactly how much paint to buy — walls, ceiling, doors, and windows accounted for. Includes 10% waste.
How It Works
Computes wall area (perimeter × height), subtracts openings, divides by coverage (350 sq ft/gallon), multiplies by coats, adds 10% waste.
Formula
Wall Area = 2(L+W) × H − Openings
Gallons = Wall Area × Coats ÷ 350 × 1.10
Example
12×14 ft room, 8 ft ceilings, 2 windows, 1 door, 2 coats:
Wall area = 366 sq ft. Gallons = 2.3 (incl. waste)
When to Use This Calculator
Use before any painting project to buy the right amount and avoid costly return trips for color-matched paint.
Common Mistakes to Avoid
- No waste factor — buy 10% extra minimum.
- One coat over dark colors — dark-to-light needs primer + 2 finish coats.
- Forgetting ceiling — calculate separately if different color.
Frequently Asked Questions
Coverage per gallon?
350–400 sq ft on previously painted surfaces. Rough/unpainted walls: 200–300 sq ft.
Do I need primer?
Use over bare drywall, going dark to light, or covering stains.
How long between coats?
Latex paint: 2–4 hours. Wait overnight for best results.
Interior vs exterior paint?
Never interchange — each has specialized additives for its environment.
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Last Updated: July 4, 2026