Renovation & Design
Precision Paint & Coverage Calculator
Paint math is perhaps the only form of trigonometry that involves wet floors, ladders, and the looming threat of a "halfway-finished" panic. Whether you're refreshing a small study in Metric (Meters/Liters) or coating a grand hall in Imperial (Feet/Gallons), calculating your surface area is the first step toward a professional result. Our tool accounts for the 3D volume of your room, the number of coats required, and the specific efficiency of your chosen paint brand.
The Geometry of a Perfect Coat
To determine how much paint you need, we must first calculate the total surface area of all four walls. This isn't just a simple length-times-width calculation; it’s a sum of two pairs of opposing planes.
// The Surface Area Formula
Total Area = 2 \times (L \times H) + 2 \times (W \times H)
Where L is Length, W is Width, and H is Height.
Understanding Coverage & Coats
Not all paints are created equal. A premium "one-coat" paint might cover 400 sq ft per gallon, while a budget-friendly option or a primer might only cover 250 sq ft. Furthermore, the porosity of your walls matters. A fresh, unprimed drywall will "drink" more paint than a previously painted surface.
Standard Coverage (Imperial)
Typically, 1 Gallon covers 350 to 400 square feet. For a standard room, this usually translates to two full coats per gallon for the average accent wall.
Standard Coverage (Metric)
Typically, 1 Liter covers 10 to 12 square meters. Professional European mixes often list this as "spreading rate" on the back of the tin.
How to Use the Tool
Choose Your System
Select either Meters/Liters or Feet/Gallons. The calculator will automatically adjust the math to match your local hardware store's inventory.
Input Room Specs
Enter the length, width, and height of the room. Note: This tool assumes a standard rectangular room. For L-shaped rooms, treat them as two separate areas.
Coats & Coverage
Enter the number of coats (standard is 2) and the coverage rate found on your paint can. The tool will calculate the total volume required, including a small buffer for spillages.