Paint Calculator
How many gallons of paint a room needs, from wall length, height, doors and windows.
- Gross wall area (sq ft)352
- Paintable area after openings (sq ft)301
- Gallons to buy (350 sq ft/gal per coat)2
Inputs used
- Total wall length (all walls)44 ft
- Ceiling height8 ft
- Doors1
- Windows2
- Coats2
About this calculator
Paintable area is the total wall length times the ceiling height, minus standard deductions for openings — about 21 square feet per door and 15 per window. A gallon of paint covers roughly 350 square feet per coat, and most jobs need two coats.
"Total wall length" means all walls added together: a 12 × 10 room has 44 feet of wall. Dark colors over light (or the reverse) may need a third coat; textured surfaces and bare drywall drink more paint than the coverage figure suggests — primer first is cheaper than an extra coat of paint.
The gallon count rounds up to whole cans. Leftover paint is worth keeping for touch-ups, so rounding up isn't waste.
Results are informational only — not financial, medical or legal advice.