Professional Paint Square Footage Calculator
Determine exactly how much paint you need for your next project.
How to Calculate Square Feet for Painting
Accurately calculating the square footage of your walls is the most critical step in planning a DIY painting project. Buying too much paint is a waste of money, while buying too little leads to frustrating mid-project trips to the hardware store and potential color matching issues.
The Basic Formula
To find the total surface area of your walls, use this formula:
Total Wall Area = 2 × (Length + Width) × Height
For example, if your room is 12 feet long, 10 feet wide, and has 8-foot ceilings:
- Length + Width = 22 feet
- 22 × 2 = 44 linear feet of wall
- 44 × 8 (Height) = 352 square feet of wall space
Subtracting Windows and Doors
You don't paint over your windows and doors (usually), so you should subtract their area from your total. Standard estimates for deductions are:
- Standard Door: 21 square feet
- Standard Window: 15 square feet
If our example room has one door and two windows, you would subtract 51 square feet (21 + 15 + 15) from your 352 square foot total, leaving you with 301 net square feet.
Accounting for Paint Coverage and Coats
A standard gallon of paint typically covers between 350 and 400 square feet. However, professional painters almost always recommend two coats for a durable, uniform finish. This means you need to double your net square footage calculation before dividing by the coverage rate.
Realistic Example Calculation
Imagine a living room that is 15′ x 20′ with 9′ ceilings. It has 2 doors and 3 windows. You plan to apply 2 coats of premium paint.
- Wall Perimeter: (15 + 20) × 2 = 70 feet
- Total Wall Area: 70 × 9 = 630 sq ft
- Deductions: (2 × 21) + (3 × 15) = 42 + 45 = 87 sq ft
- Net Area per Coat: 630 – 87 = 543 sq ft
- Total Area for 2 Coats: 543 × 2 = 1,086 sq ft
- Gallons Needed: 1,086 ÷ 350 ≈ 3.1 gallons
In this scenario, you should purchase 4 gallons to ensure you have enough for touch-ups.