Paint Calculator: How Much Paint Do I Need?

Estimate Paint Amounts Based on Square Footage

Pouring a can of paint into a tray

The Spruce / Margot Cavin

This paint coverage calculator makes calculating the amount of paint you'll need for your project nearly automatic. Your role in the process involves just a few elements:

  • Measure the height and width of each wall to be painted.
  • Add in the number of windows and doors in the space.
  • Decide if you want to paint the ceiling.
  • Decide how many coats of paint you'll apply.
  • Press the "Calculate" button.

Please ensure you are using the most up-to-date version of your web browser to avoid potential errors. All mathematical computations occur invisibly to produce a reasonably accurate estimate of how much paint you'll need.

Using the Paint Calculator

The paint calculator helps plan an interior or exterior home painting project. It automates calculations you could make yourself using fairly basic math skills. The calculator makes several basic assumptions in its computations:

  • One gallon of paint is assumed to cover approximately 350 square feet.
  • A standard door accounts for about 20 square feet.
  • An average window accounts for about 15 square feet.

Estimate the Amount of Paint

Room Shape and Wall Dimensions

Choose the room shape, then count the number of walls in your room. Enter the length and width of each wall. Rectangular and square rooms have four walls to be painted. L-shaped rooms have six wall surfaces, while others may have more.

Windows and Doors

Count the number of windows and doors in the room and enter them in the calculator tool. The calculator will subtract those spaces from the square footage in the paint estimate.

Ceiling Paint

Determine if you are painting the ceiling. Click the checkbox for “Ceiling Paint” on the calculator. Ceiling painting will be calculated as a separate item.

Number of Coats

Select how many coats you plan to use to paint the room. The calculator automatically defaults to two coats. It's typical to coat most walls twice to ensure against bare or thin spots and to create a seal or barrier that makes the wall easier to clean. You might want to change the default if:

  • Using high-quality paint with more pigments and resins; these specialty paints may only require one coat.
  • Refreshing a wall with the same paint color; one coat is great for a touch-up coat.
  • Planning ahead; by using three coats, the paint job will last longer than two coats.

Editing Your Entries

Editing your calculations is easy at any point:

  • Edit square footage measurements: Update the width or height fields you want to change and press “calculate” again. To add extra walls and their measurements, press the plus sign next to “add wall.” To remove walls, press the trash can icon.
  • Start over: To get a new estimate, select your desired room shape, and enter the new measurements. Then press “calculate” again. Note: Doing so will delete your current paint calculation, so note your results.

Room Examples for Painting

For example, imagine you have a 12-foot by 12-foot room with standard 8-foot-high ceilings. Here's how to use the calculator:

  1. Pick a room shape; in this case, a square.
  2. Enter the length and height of each wall; in this example, each wall is 12 feet by 8 feet.
  3. Decide if you want to paint the ceiling; in this example, do not checkmark it.
  4. Enter the number of windows and doors in the room; in this example, select two windows and one door.
  5. Decide if you want to apply one, two, or three coats of paint; keep the default of two coats.
  6. Hit the "Calculate" button.

Automatically, the paint calculator gives you an estimate of 2 gallons of paint for applying two coats to a 12 x 12 room with an 8-foot ceiling with two windows, one door, and the painting of the ceiling is not included.

Here's another example: You have a shed or garage with exterior walls that are 25 feet long and 10 feet tall, for a total of 1,000 square feet. Because the existing walls are weathered and in poor shape, they're likely to absorb a lot of paint, and you estimate that three coats will be necessary. There are three windows and one door in your shed or garage. If you enter all these values into the paint calculator, you are given an estimate of 9 gallons to paint your structure.


You can copy the provided embed code if you'd like to add this paint calculator to your website or blog. Once you've finalized your measurements and other specifications, click or tap "Embed This Tool" to generate a code that you can insert into your website