Paint Calculator
Calculate the volume of paint required for a room or wall. Automatically deducts doors and windows, and calculates gallons and liters needed for multiple coats.
Calculation Results
Total surface area to paint, with doors and windows deducted.
Surface area multiplied by the number of coats.
Volume of paint needed in gallons.
Volume of paint needed in liters.
How This Calculator Works
To calculate paint requirements:
- Enter the total length of all walls combined (for a 10ft x 12ft room, total length is 10+10+12+12 = 44 feet).
- Enter the height of your walls (typically 8 or 9 feet in residential houses).
- Enter the count of doors and windows inside the room so their areas can be subtracted.
- Choose the number of coats (2 coats is recommended for a high-quality finish).
- Adjust the coverage rate if you have a specialized prime/paint.
Formula & Calculations
The total area of the walls is first computed by multiplying length by height:
Gross Area = Wall Length × Wall Height
Deductions are then made for openings. Standard dimensions are assumed:
- Each door subtracts 21 square feet (standard 3ft × 7ft door).
- Each window subtracts 15 square feet (standard 3ft × 5ft window).
The net painting area is multiplied by the number of coats and divided by the paint's coverage rate (typically 350 sq ft per gallon):
Gallons = (Net Area × Coats) / Coverage Rate
Step-by-Step Calculation Examples
Typical Bedroom (12ft x 15ft room)
Painting walls in a 12ft x 15ft room with 8ft ceilings, containing 1 door and 2 windows, applying 2 coats.
- length: 54
- height: 8
- doors: 1
- windows: 2
- coats: 2
- coverage: 350
- net_area: 381.0 sq ft
- total_paint_area: 762.0 sq ft
- gallons: 2.18 gal
- liters: 8.24 L
Frequently Asked Questions
How much area does one gallon of paint cover?
A standard gallon of paint covers between 350 and 400 square feet on smooth, primed walls. Textured walls or unprimed drywall will absorb more paint, reducing coverage to 250-300 square feet.
Should I buy a separate primer?
Yes, if you are painting new drywall, switching from a dark to a light color, or painting over glossy surfaces. A primer seals the surface and improves paint adhesion, reducing the overall coats needed.