Paint Calculator
Estimate how much paint you need for your walls — add each wall, set coats, and account for windows and doors.
How to use
- Enter the width and height of each wall you plan to paint.
- Click + Add another wall to include more walls.
- Choose your unit system — Imperial (feet, gallons) or Metric (meters, liters).
- Set the number of coats you plan to apply (default is 2).
- Enter the paint coverage — how many square feet per gallon or square meters per liter (check the paint can).
- Optionally subtract the total area of windows and doors.
- Click Calculate to see the total area and how much paint to buy.
When people use this
- Painting a single room or a whole house.
- Estimating paint quantity before starting a DIY project.
- Planning for multiple coats on dark or porous surfaces.
- Figuring out how much paint to buy when subtracting windows and doors.
Examples
Standard 12×8 wall. One 12 ft × 8 ft wall with 2 coats and 350 sq ft/gallon coverage needs 0.55 gallons — round up to 1 gallon.
Whole room (4 walls). Four walls each 12 ft × 8 ft = 384 sq ft gross. Minus 20 sq ft of windows and 16 sq ft of doors = 348 sq ft net. 2 coats = 696 sq ft. At 350 sq ft/gallon, that is 1.99 gallons — buy 2 gallons.
Metric example. Three walls 3 m × 2.4 m = 21.6 m² gross. Minus 2 m² of windows = 19.6 m² net. 2 coats = 39.2 m². At 10 m²/L coverage, that is 3.92 liters — buy 4 liters.
Frequently asked questions
How much paint does a gallon cover?
Standard paint covers about 350–400 sq ft per gallon (10–12 m² per liter), but check the specific product — masonry, exterior, and primer cover differently.
How do I measure a wall that is not a plain rectangle?
Break it into rectangles (flat parts) and triangle or trapezoid sections, calculate each, and add them. For sloped ceilings, measure the actual surface length, not the floor length.
How many coats should I plan for?
Start with two coats for most interior walls for even coverage and color depth. Light colors over white may need only one; dark or drastic changes may need three.
What about windows, doors, and trim?
Subtract the window and door areas using the calculator fields. Paint them separately and add a little extra for the trim and edges around them.