Room Wall Paint Calculator

Find out how much paint you will need to paint a room in the fastest way possible. This is the quickest wall paint calculator online!

Paint Calculator – Try It!

sq. feet sq. inches

feet inches


feet inches


meters (metres)


meters (metres)

1st Wall: feet inches feet inches
1st Wall: meters (metres) meters (metres)

You will need...


of paint per coat (for the calculated total area of square feet.)

You will need...


of paint per coat (for the calculated total area of m2)

How It Works

Our wall and room paint calculator is designed to be as simple as possible yet an accurate way to estimate how much paint you will need to paint a room or a wall (or a few walls). We are proud to have developed a formula that allows you to get a quick estimate based only on as much data (measurements) you have available. So, you can calculate how much paint you need if you have:

  • Your room area.
  • The width of the two perpendicular walls of your room.
  • Or if you have complete measurements for every wall (width, height), every door, and window in your room.

The calculator then gives you the estimate of paint in gallons (or liters).


Obviously, the more data you enter into the calculator, the more accurate the results. Otherwise, we make educated guesses to give you an estimate (based on industry averages). In any case, it’s pretty accurate, and you can get the fastest estimation possible to get an idea of how much paint you need.


If you don’t provide the detailed measures of the room, we will make these assumptions:

  • If you only have the room area (in square feet or square meters) we will assume a rectangular room (industry average ratio of about 3:4) and the height of the ceiling of 4 feet (or 2.74 meters). We also assume the room has a door (3×8 feet) and a window (3×5 feet). Finally, we add an overhead of 10% for unexpected paint use during painting. Surprisingly, this gives quite an accurate estimate based on our trials. Most of the time, this is all you need.
  • If you have the width of perpendicular walls of a rectangular room, we only assume the height of the ceiling and the sizes of a door and a window (plus the 10% overhead). This estimation mode is more accurate because we can calculate the exact perimeter of a rectangular room without making guesses about its shape.
  • If your room doesn’t quite fit the description of an average room as we assumed above, you will get better results if you provide us with detailed measurements. In this case, you can enter the measurements of each wall (as many walls as you need), as many doors and windows as you have, and specify the exact measurements of each. Use this mode if you only need to paint a single wall too.
  • Finally, we assume 1 gallon of paint is needed to cover 400 square meters of area in one coat (or 1 liter for 9.8 m2 in the metric mode.)

How to Use It

First, choose from the following measurement systems:

Metric or imperial measurement system (imperial is selected by default.)

Quick Estimation

It works in 2 modes as well: by area or by dimensions.

Estimating by area you only need to provide the total area of the room.

Estimating by dimensions you need to provide the widths of the perpendicular walls.

Detailed Measures

Add the measurements of each wall. Add and remove walls, windows, and doors by using the “Add/remove” buttons.

Clicking the Calculate button immediately gives you the result of the estimated paint needed for a single coat (the calculated area is indicated.)


  • If the walls have baseboards, trim, or molding, subtract the height of those from the height of each wall affected.
  • If the ceiling is sloped, use the average height of the ceiling (highest point plus lowest point divided by two.)