Paint Calculator
Estimate how much paint you need for a room, wall, ceiling, or other rectangular surface.
Enter your surface dimensions, subtract doors and windows, choose the number of coats, and enter your paint coverage to get an estimated paint quantity.
Calculate Paint Needed
Enter dimensions in feet and paint coverage in square feet per gallon.
Surface Dimensions
Doors & Windows
Enter the total area of doors and windows that will not be painted.
Paint Settings
Paint Estimate
How Does the Paint Calculator Work?
The calculator first estimates the total wall area using the room length, width, and wall height. It then subtracts the area of doors and windows that will not be painted.
The remaining paintable area is multiplied by the number of coats. Finally, the total coverage area is divided by the coverage provided by one gallon of paint.
Paint Needed = Paintable Area × Coats ÷ Coverage
How to Calculate Wall Area
For a rectangular room, the total wall area can be calculated using the room perimeter and wall height.
Wall Area = 2 × (Length + Width) × Height
For example, a room that is 20 feet long, 15 feet wide, and 8 feet high has:
2 × (20 + 15) × 8 = 560 sq ft
If the room has 40 square feet of doors and windows, the paintable wall area is:
560 − 40 = 520 sq ft
Understanding Paint Coverage
Paint coverage tells you approximately how much surface area one gallon of paint can cover. The actual coverage depends on the specific product and the surface being painted.
Always check the manufacturer's coverage information on the paint container before purchasing paint.
| Paint Coverage | Meaning |
|---|---|
| 300 sq ft/gal | One gallon covers approximately 300 sq ft |
| 350 sq ft/gal | One gallon covers approximately 350 sq ft |
| 400 sq ft/gal | One gallon covers approximately 400 sq ft |
Paint Calculator Example
Suppose a room is 20 feet long, 15 feet wide, and 8 feet high. The total wall area is:
2 × (20 + 15) × 8 = 560 sq ft
If doors and windows account for 40 square feet, the paintable area becomes 520 square feet.
With 2 coats and paint coverage of 350 square feet per gallon:
520 × 2 ÷ 350 ≈ 2.97 gallons
The calculator reports the mathematical estimate and can help you determine an appropriate amount to purchase.
What Can Affect Paint Quantity?
The calculated quantity is an estimate. Actual paint usage can vary depending on the surface and application.
- Surface texture and porosity
- Paint type and product coverage
- Number of coats required
- Existing wall color
- Application method
- Doors, windows, and other unpainted areas
How to Use the Paint Calculator
- Enter the room length in feet.
- Enter the room width in feet.
- Enter the wall height in feet.
- Enter the combined area of doors and windows.
- Enter the number of coats you plan to apply.
- Enter the paint coverage shown on the product label.
- Click Calculate Paint to see the estimated paint quantity.
Important Note About Paint Estimates
Paint calculators provide an estimate rather than an exact purchase requirement. Different paints can have different coverage rates, and real-world application can use more or less paint than the theoretical calculation.
For the most accurate estimate, use the coverage information supplied by the paint manufacturer and account for the actual condition of your surfaces.
Frequently Asked Questions
How much paint do I need for a room?
It depends on the total paintable surface area, number of coats, and paint coverage. Enter these values into the calculator to get an estimate.
Does the calculator subtract doors and windows?
Yes. You can enter the combined area of doors and windows, and that area is subtracted from the total wall area.
Should I include the ceiling?
The main calculation estimates wall paint. If you also want to paint the ceiling, its area can be calculated separately and added to the total paintable area.
How many coats of paint should I use?
The required number of coats depends on the paint product, surface condition, existing color, and desired finish. Follow the manufacturer's instructions for your specific product.
Is the paint estimate exact?
No. It is a mathematical estimate based on the information you provide. Actual paint usage can vary because of surface texture, absorption, application technique, and product coverage.