Paint Calculator
Find out how many gallons of paint you need to cover your room's walls.
- Paint to buy2 gallon(s)
- Exact gallons1.9 gal
- Paintable wall area333 sq ft
- Total area with coats666 sq ft
How to use
- Enter the room length, width and wall height in feet.
- Enter how many doors and windows to subtract, and how many coats.
- Read the paintable area and gallons of paint to buy.
About this calculator
This paint calculator estimates the paintable wall area of a room and converts it to gallons. It takes the wall perimeter times the height, subtracts a standard 21 sq ft per door and 15 sq ft per window, then multiplies by the number of coats. One gallon of wall paint covers roughly 350 square feet per coat. The result is rounded up because you can only buy whole cans, and it is wise to keep a little extra for touch-ups. For brand-new drywall or a big color change, plan on two coats.
🧮 How it's calculated
- 1Step 1 — Wall perimeter: Perimeter = 2 × (Length + Width)
- 2Step 2 — Gross wall area: Gross = Perimeter × Wall Height
- 3Step 3 — Subtract openings: Net area = Gross − (Doors × 21 ft²) − (Windows × 15 ft²)
- 4Step 4 — Apply coats: Total area = Net area × Number of coats
- 5Step 5 — Convert to gallons: Gallons = Total area ÷ 350 (coverage per gallon)
Gallons = (Wall area - doors - windows) x Coats / 350 sq ft per gallon.
Frequently asked questions
How much does a gallon of paint cover?+
About 350 square feet per coat for most interior wall paints on a smooth, primed surface. Rough or porous surfaces cover less.
How many coats of paint do I need?+
Two coats is standard for good coverage and durability, especially over new drywall or when changing colors. One coat may do for minor refreshes.
Does this include the ceiling?+
No, this estimates walls only. Calculate the ceiling separately as length x width, divided by 350 sq ft per gallon.