Here’s How to Find How Much Paint You Need for Your Project

Marwa Hasan
Written by Marwa Hasan
Updated February 23, 2022
Woman painting a wall
Photo: svetikd / E+ / Getty Images


  • One gallon can of paint covers up to 400 square feet.

  • A simple math equation will help you determine how much paint you need.

  • A 300-square-foot room with a window will need an average of 1 1/2 gallons for two coats of paint.

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If you want to give your space a facelift, painting your rooms is an easy, DIY-friendly way to totally transform your home. But once you have that perfect shade picked out, how do you know how many cans of paint you need to buy? With a little bit of math, you can figure out exactly what you need—and not have to deal with disposing of leftover paint.

Determining Paint Per Square Foot

While some paint formulas and wall textures may require more specific amounts, here are some basic facts of paint coverage:

  • One gallon of paint covers up to 400 square feet. This is enough to cover a small room, like a bathroom.

  • Two gallons of paint cover up to 800 square feet, enough to cover an average-sized room in two coats of paint.

  • Three gallons of paint cover up to 1,200 square feet, enough to cover a couple of average-sized rooms or one large room.

  • Four gallons of paint cover up to 1,600 square feet, enough to cover several average-sized rooms.

How to Estimate the Space’s Square Footage

Before you begin painting the walls, you need to estimate the amount of paint you’ll use. Figure out how many cans of paint you need by calculating each surface you want to paint.

Solid Walls

A paint brush into a large tin of pink paint
Photo: Catherine Falls Commercial / Moment / Getty Images

To calculate the square footage of solid walls: 

  • Measure the length of all walls.

  • Measure the room’s height from floor to ceiling, minus any trim, baseboards, and crown molding. 

  • Multiply the length by the height; the number you get is the room’s square footage. 

For example, a room with a solid wall that measures 10-by-10 feet and a second solid wall total 12-by-10 feet, the two solid walls together would be 220 square feet.

Walls with Doors or Windows

To calculate the square footage of a wall with a door or a window:

  • Measure the length and height of a wall to find its total square footage.

  • Measure the door/window area, including the window frame and glass, and leave out any molding. 

  • Subtract the area of each door/window from the total wall area.

For example, for a 12-by-10-foot wall with one 4-by-6-foot window, you will have 96 square footage of a wall to paint.


Whether you’re using the same color or a different color than the walls when painting the ceiling:

  • Measure the length and width of the room’s ceiling.

  • Multiply the measurements to find the square footage. 

If you’re using the same color, treat the ceiling as a fifth wall. If you’re using a different color, estimate the square footage and multiply by two to account for a second coat.

Frames, Trims, or Molding

If you’re painting your trim a different color than the walls:

  • Measure the length and width of each trim, crown molding, window, and door frame separately from the rest of the room.

  • Multiply the length by the width to get the square footage of the area to be painted.

Double-check your calculation using HomeAdvisor’s paint calculator.

So, How Much Paint Should You Buy?

Divide the total number by the approximate coverage of one gallon of paint (400 square feet per gallon). This will give you the number of gallons of paint you’ll need for one coat. 

The rule of thumb is to apply two coats of paint on walls and one on the ceiling. Multiply this number by two to estimate how much paint you’ll need to give them two coats. Round up uneven numbers and purchase slightly more paint for waste allowance. This will keep you from making multiple trips to the home improvement store for more paint, and save you some for future touch-ups.

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