🧱 Paint Calculator
Painting a room? Don't guess — calculate exactly how many gallons you need. Enter your room dimensions, doors, windows and coats. A standard 12x12 room with 8ft ceilings needs about 2 gallons for two coats.
No sign-up, instant results — your measurements stay in your browser.
How to use this calculator
Enter your room dimensions and the calculator subtracts doors and windows, then tells you exactly how many gallons to buy.
- Enter Room length and width in feet (e.g. 12 x 12).
- Enter Ceiling height (standard is 8 ft).
- Enter number of Doors and Windows to subtract.
- Choose Coats of paint and press Calculate.
Planning Your Project With the Paint Calculator
Measure twice and enter exact dimensions: material estimates are only as good as the measurements behind them. The Paint Calculator gives you net quantities; add 10-15% for waste, then confirm pricing with local suppliers before you commit.
Frequently asked questions
How many gallons of paint for a 12x12 room?
About 2 gallons for two coats. A 12x12 room with 8ft ceilings has ~384 sq ft of wall area; minus one door and two windows leaves ~333 sq ft. At 350 sq ft per gallon, that's ~1 gallon per coat.
How much area does one gallon cover?
Approximately 350 square feet per coat for interior wall paint. Primer or dark colors may need more.
Should I buy extra?
Round up to the next full gallon — you'll want extra for touch-ups later. Paint stores can match the color if you bring the can.
How much extra material should I order?
Order 10-15% extra for cuts, breakage and mistakes; complex layouts with many angles need closer to 15%. The Paint Calculator gives you the exact net quantity, so multiply its result by 1.10 to 1.15 for your order amount.
Does this Paint Calculator account for waste?
The Paint Calculator calculates the precise net quantity your dimensions require. Waste factors vary by project, so add your own 10-15% margin on top of the result for the final purchase quantity.
What if my project area is an irregular shape?
Break irregular areas into rectangles, triangles and circles, run each through the Paint Calculator separately, then add the results. For L-shapes, two rectangles usually suffice; for curves, approximate with a rectangle plus a triangle.
How accurate are the cost estimates?
Material quantities from the Paint Calculator are mathematically exact for the dimensions entered. Costs vary by supplier and region, so treat the cost figure as a planning estimate and confirm with local quotes before budgeting.