Paint Calculator

This calculator relies on a series of straightforward geometric and algebraic formulas to evaluate your surface area requirements. First, it computes the gross wall area by finding the total perimeter of the room and multiplying it by the room height: Gross Wall Area = (Room Width + Room Length) × 2 × Room Height. Next, it subtracts non-paintable spaces by calculating the total area of doors and windows using their respective dimensions and quantities. The net paintable area is then multiplied by your desired number of coats and divided by the paint efficiency rating (square feet per gallon) to determine the total amount of paint required. Finally, multiplying the total volume of paint by the cost per unit yields your overall project budget.

Imagine you want to paint a living room that measures 15 feet long by 10 feet wide, with standard 9-foot ceilings. First, we find the gross wall area: (10 + 15) × 2 × 9 = 450 square feet. Next, suppose the room has 1 standard door measuring 7 feet by 3 feet (21 sq ft total) and 2 windows measuring 4 feet by 3 feet each (24 sq ft total). The combined non-paintable area is 45 square feet. Subtracting this from the gross area gives a net paintable area of 405 square feet. If you plan to apply 2 coats of paint, and your paint covers 350 square feet per gallon, the calculation for the amount of paint is (2 × 405) / 350 = 2.31 gallons. Rounded up, you will need 3 gallons. At a cost of $45 per gallon, your total paint cost will be 3 × $45 = $135.

To ensure flawless results, always round your final paint volume up to the nearest whole gallon to account for touch-ups, spills, and roller absorption. When measuring doors and windows, measure the entire frame trim if you intend to paint the casing as well. Lastly, always factor in paint efficiency ratings provided by manufacturers, as textured walls or highly porous surfaces often absorb more product than smooth drywall.