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.
Quick reference
Gallons of paint by wall length and coats
Gallons for 8 ft ceilings, counting full wall area with no door or window deductions (350 sq ft/gallon per coat).
| Total wall length (all walls) | 1 | 2 | 3 |
|---|---|---|---|
| 30 ft | 1 | 2 | 3 |
| 40 ft | 1 | 2 | 3 |
| 50 ft | 2 | 3 | 4 |
| 60 ft | 2 | 3 | 5 |
| 70 ft | 2 | 4 | 5 |
| 80 ft | 2 | 4 | 6 |
| 100 ft | 3 | 5 | 7 |
| 120 ft | 3 | 6 | 9 |
Frequently asked questions
How much paint do I need for a 12x12 room?
A 12 × 12 room has 44 feet of wall, and at an 8 ft ceiling that is 352 square feet. Subtracting one door and two windows leaves about 301 square feet, so two coats need roughly 602 square feet of coverage — two gallons at 350 square feet per gallon per coat.
How many square feet does a gallon of paint cover?
About 350 square feet per coat on a smooth, previously painted wall. Bare drywall, textured surfaces and deep color changes absorb more, so treat 350 as an upper estimate and prime first when covering a big color shift.
How many gallons do I need for two coats?
Two coats double the paint required: multiply the paintable wall area by two and divide by 350. Most repaints need two coats for an even finish, and dark-over-light or light-over-dark jobs sometimes need a third.
Should I subtract doors and windows?
For accuracy, yes — this calculator deducts about 21 square feet per door and 15 per window. On a small room the difference is only a fraction of a gallon, but it adds up across a whole house.
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