Paint Calculator
Interior · Updated July 2026
Enter your room's perimeter, wall height, number of doors and windows, and coats to find how many gallons of paint you need.
Your project
Results
Estimates only. Add extra for waste and confirm with your supplier.
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How much paint do I need?
One gallon of paint covers about 350 sq ft per coat. Calculate wall area, subtract doors and windows, multiply by the number of coats, then divide by 350.
How much paint per coat
A gallon covers about 350 sq ft per coat on smooth, primed walls. Calculate wall area (perimeter × height), subtract doors and windows, and multiply by the number of coats — most colors need two.
When you need more
Porous, textured, or previously unpainted surfaces drink more paint, and dark-to-light color changes often need an extra coat or a tinted primer. Buy all your paint in one batch so the color is consistent across the room.
How to use this calculator
- 1Add up the length of every wall for the perimeter.
- 2Enter wall height, doors, windows, and coats.
- 3The calculator subtracts openings and gives gallons needed.
Frequently asked questions
How much does a gallon of paint cover?
A gallon typically covers 350–400 sq ft with one coat on a smooth, primed surface.
How much does a gallon of paint cover?
About 350–400 sq ft per coat on a smooth, primed surface.
How many coats of paint do I need?
Two coats is standard; dramatic color changes or bare surfaces may need a primer plus two coats.
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