Paint Calculator
Buying the right amount of paint saves trips to the store and money. This calculator estimates gallons needed based on your room dimensions, accounting for doors and windows you won't be painting.
Enter Your Measurements
Results
Enter your measurements to see results
How to Use This Calculator
- Measure the room length and width in feet.
- Measure the wall height (usually 8 or 9 feet).
- Count the number of standard doors and windows.
- Select number of coats (2 is recommended for most jobs).
- Review the gallons needed.
How Paint Calculation Works
One gallon of paint covers approximately 350–400 square feet of smooth wall with one coat. This calculator uses 350 sq ft as a conservative estimate. It subtracts 21 square feet per standard door (3×7 ft) and 15 square feet per average window (3×5 ft) from the total wall area. Textured walls, dark-to-light color changes, and bare drywall may require an extra coat.
Formula
Wall area = 2 × (Length + Width) × Height. Subtract ~21 sq ft per door and ~15 sq ft per window. Divide paintable area by 350 sq ft/gallon coverage, then multiply by number of coats.
Frequently Asked Questions
How many gallons of paint for a 12×12 room?
A 12×12 room with 8-foot ceilings, 2 doors, and 2 windows needs about 2 gallons for 2 coats. This covers approximately 312 square feet of paintable wall area.
How much does a gallon of paint cover?
One gallon of interior paint covers 350–400 square feet on smooth surfaces with one coat. Rough or textured surfaces may only get 300 square feet per gallon.
Do I really need two coats of paint?
In most cases, yes. Two coats provide even coverage, true color, better durability, and hide the previous color. You might get away with one coat if you're painting the same color or using a high-quality paint-and-primer combo over a light-colored wall.
Should I buy extra paint?
Yes, buy about 10% more than calculated. You'll want extra for touch-ups, and paint colors can vary slightly between batches. Most stores accept returns on unopened cans.