Paint Calculator
Estimate how many gallons of paint you need for walls based on room dimensions, doors, and windows.
Total Wall Area—
Paintable Area—
Paint Needed—
How to Calculate Paint Needed
Wall Area = 2 × (Length + Width) × Height
Paintable Area = Wall Area − (Doors × 20 ft²) − (Windows × 15 ft²)
Gallons = (Paintable Area × Coats) ÷ 350
Paintable Area = Wall Area − (Doors × 20 ft²) − (Windows × 15 ft²)
Gallons = (Paintable Area × Coats) ÷ 350
Standard paint covers about 350 sq ft per gallon. A door averages 20 sq ft and a window averages 15 sq ft of unpainted area.
Example:
Room: 15 ft × 12 ft, 8 ft high, 1 door, 2 windows, 2 coats
Wall area = 2 × (15 + 12) × 8 = 432 sq ft
Paintable = 432 − (1×20) − (2×15) = 382 sq ft
Gallons = (382 × 2) ÷ 350 = 2.18 gallons (buy 3)
Room: 15 ft × 12 ft, 8 ft high, 1 door, 2 windows, 2 coats
Wall area = 2 × (15 + 12) × 8 = 432 sq ft
Paintable = 432 − (1×20) − (2×15) = 382 sq ft
Gallons = (382 × 2) ÷ 350 = 2.18 gallons (buy 3)
Coverage by Paint Type
Flat/Matte: 350–400 sq ft/gal | Eggshell/Satin: 350 sq ft/gal | Semi-gloss: 300–350 sq ft/gal | Primer: 200–300 sq ft/gal
FAQ
How many coats do I need?
Two coats are standard for most interior walls. Use three coats when painting over a dark color with a lighter one, or when using red/deep tones.
Should I buy extra paint?
Always round up to the nearest whole gallon. Buy an extra quart for touch-ups later, as color matching a dried batch can be difficult.
Last updated: 2026-08-08