What Is the Paint Calculator with Multiple Coats?
This Paint Calculator estimates how much paint you need to cover a wall (or several walls totaling a given area) when applying more than one coat. It works with any unit system as long as your area and coverage rate use the same units — for example square feet of area with coverage in square feet per gallon, or square meters with square meters per liter.
How to Use It
Enter the total wall width and height to define the area, or treat the width × height as your full painted surface. Set the number of coats (most projects use 2). Enter the coverage rate of your specific paint — this is printed on the can (commonly around 350–400 sq ft per gallon, or about 10 m² per liter). The calculator multiplies area by coats, divides by coverage, and tells you the amount of paint required.
The Formula Explained
The core equation is:
$$\text{Paint} = \left\lceil \frac{\text{Width} \times \text{Height} \times \text{Coats}}{\text{Coverage}} \right\rceil$$
Wall area is simply \(\text{Width} \times \text{Height}\). Each coat repaints the full area, so two coats need twice the paint of one. Dividing the total painted area by the paint's coverage rate gives the number of units (gallons or liters) you must buy.
Worked Example
Suppose a wall is 20 ft wide and 8 ft tall, giving 160 sq ft. You want 2 coats and your paint covers 350 sq ft per gallon. Total painted area = \(160 \times 2 = 320\) sq ft. Paint needed = \(320 \div 350 \approx 0.91\) gallons — so you'd buy 1 gallon.
FAQ
How many coats do I need? Two coats is standard for even color and durability. Use one coat only for touch-ups, and three when painting a light color over a dark surface.
Should I round up? Yes. Always buy a little extra to account for spills, touch-ups, and uneven, textured, or porous surfaces that absorb more paint.
Does this include doors and windows? No. For accuracy, subtract the area of large openings from your wall area before entering it, or simply leave them in for a small safety margin.
