What Is a Paint Calculator?
Tom, a homeowner in Denver, decides to repaint his living room. He heads to the hardware store and stares at the wall of paint cans. One gallon, five gallons, quarts, liters. He has no idea how much to buy. Buy too little and he makes a second trip mid-project, risking a slight color mismatch from a different batch. Buy too much and he wastes money on paint he will never use. He measures his walls, enters the numbers into a paint calculator, and sees he needs 2 gallons for two coats. Problem solved in under a minute.
A paint calculator estimates the amount of paint required to cover a given wall area. It takes wall dimensions, subtracts the area of doors and windows that do not need painting, and multiplies by the number of coats. The result is converted to gallons or liters based on standard paint coverage rates. For calculating tile needs for a similar project, try our Tile Calculator.
What This Calculator Does
This paint calculator computes the paintable wall area by subtracting standard door and window areas from the total wall area, then multiplies by the number of coats to get the total coverage needed. It supports both imperial (feet, gallons) and metric (meters, liters) units and reports paint needed in both gallons and liters.
- Inputs: Wall length, wall height, number of doors, number of windows, number of coats, and measurement unit
- Outputs: Paintable area, total area with coats, and paint needed in gallons and liters
How the Calculation Works
Paintable area = (wall length x wall height) - (doors x door area) - (windows x window area)
Total area = paintable area x number of coats
Gallons needed = total area / 350 sq ft per gallon
Liters needed = total area / 10 m2 per liter
The calculator uses standard coverage rates of 350 square feet per gallon and 10 square meters per liter, which are typical for interior wall paint with a roller. Standard door area is assumed at 21 square feet (3 ft x 7 ft) in imperial or 1.8 square meters (0.9 m x 2 m) in metric. Standard window area is assumed at 12 square feet (3 ft x 4 ft) or 1.08 square meters (0.9 m x 1.2 m). The final paint quantity is rounded up to the nearest whole unit for purchasing.
How to Use the Calculator
- Select your measurement unit (imperial or metric)
- Enter the total wall length and wall height of the room
- Enter the number of doors and windows to subtract from the paintable area
- Select the number of coats (two is recommended for most projects)
- The paint needed in gallons and liters updates instantly
- Copy the result using the copy button if needed
Limitations of This Calculator
This calculator assumes standard door and window sizes and a flat paint coverage rate. Actual coverage varies by paint type, brand, surface texture, application method, and color change. Porous surfaces like fresh drywall or unpainted plaster absorb more paint and may require a primer coat. Dark colors over light walls may need fewer coats, while light colors over dark walls may need three or more. The calculator does not account for ceilings, trim, or baseboards, which require separate calculations. For calculating square footage of a space, use our Square Footage Calculator or Concrete Calculator for foundation projects.