About the paint calculator
Paint coverage depends on the product and the surface, so this calculator uses the coverage printed on your paint can instead of a generic figure. Enter your total wall length and height, subtract openings, choose your number of coats, and you’ll see exactly how much to buy.
It works for one wall or a whole room. Trim, doors, and ceilings use different paints and are calculated separately.
How to use this calculator
- Measure the length of each wall and add them together.
- Enter the wall height.
- Count doors and windows; adjust their sizes under Options if yours differ.
- Choose the number of coats and enter the coverage from the paint label.
Worked examples
- Walls: 4 × 12 = 48 ft long, 8 ft high = 384 sq ft
- Subtract a 21 sq ft door and a 15 sq ft window: 348 sq ft
- Two coats: 696 sq ft
- Label coverage 350 sq ft/gal: 696 ÷ 350 = 1.99
Buy 2 gallons.
Measurement guidance
Measuring walls
Measure wall length along the baseboard. For rooms with vaulted ceilings, split the wall into a rectangle and a triangle.
Primer
Primer has its own coverage. Calculate it as a separate one-coat job using the primer’s label.
Frequently asked questions
How much does a gallon of paint cover?
It varies by product; many labels list a range of a few hundred square feet per gallon. Use the figure on your can.
Do I need two coats?
Two coats give the most even color, especially with color changes. Some paint-and-primer products may cover in one coat on similar colors.
Should I subtract doors and windows?
Yes, for large openings. For small rooms, many people skip it and keep the extra paint for touch-ups.