How Do I Calculate the Quantity of Paint I Need for My House Painting?

Staring up at the paint with a bewildered look on one’s face is a common sight to see in any painting store. You have finally figured out the color paint you need, but how much will you need to complete your house painting project? Fortunately, with some simple math, you can determine how much paint you need. 

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How Much Paint Do I Need for My Walls?

To determine how much paint one will need to cover their walls, we recommend doing the following. 

Step 1: Measure the length of the walls that need to be painted, from end to end. This will give you the perimeter of the room.

Step 2: Measure the height of all the walls that need to be painted. 

Step 3: Multiple the perimeter by the height. This will give you the square footage of the room. 

Step 3.5 (Optional): Multiple this number by however many coats you want to paint. Typically, two coats are recommended. 

Step 4: Divide the square footage by 400. 400 is the approximate coverage a single can of paint will provide for one coat. 

How Do I Calculate Paint for Windows & Doors?

Of course, most house painting projects aren’t just big walls; there are obstacles in the way, such as windows and doors. To adjust the calculations, the painter must measure the length and width of the doors and windows, calculate their square footage, and subtract it from the total. Of course, one wants to do this before determining coat amounts! See the example coming up!

Painting a Bedroom Calculation Example:

Let’s take a look at an example. The average size of a bedroom in U.S. homes is 14 feet by 16 feet, a total of 224 square feet. 

Now, let’s assume that they have two windows and one door. Standard-size windows are 15 square feet, and doors are 20 square feet. Therefore, we would go 15+15+20 = 50. 

That means we must take the 224 square feet of the room and subtract 50, leaving us with 174 feet of paintable space. 

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If a homeowner was completing a house painting project, they would want to paint two costs in the bedroom, doubling the square footage to 348 square feet. When we divide that by the average paint can coverage of 400 feet, the homeowner would need 0.87 gallons of paint. Therefore, buying a single gallon of paint for this house painting project would likely cover the whole room with some extra to spare! 

Note: Check out our Painting Calculator to estimate both the amount of paint and the price to hire Paintmaster Services, Inc. to complete your interior painting project!

How Much Primer Do I Need for my Interior Painting Project?

Primer is used to help new paint adhere to a wall better, commonly used on walls that are porous, unpainted, making a dramatic color switch, or when covering up stains. When one uses primer, it doesn’t affect how much paint one will need, as applying two coats on top of the primer is still recommended. 

However, the math is slightly different if one is trying to calculate how much primer to buy. Primer cans hold less volume than paint cans, covering only 200-300 square feet compared to a paint can’s 400. Therefore, we recommend replacing “400” with “200” in the equation above to get an appropriate amount.  

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How Much Paint Do I Need for Trim?

When completing a house painting project, the room’s baseboards, window trim, door trim, and crown molding are typically painted a different color from the walls and ceilings to provide a pop of style. Determining the amount of paint you will need for trim follows the same concept above.

First, calculate the square footage by multiplying the length and width of all the trim. Do note that if there are varying sizes of trim, they will need to be calculated separately and then added together. 

Second, divide the total square footage by 400 to get the gallons required. We want to note that most standard rooms require less than a gallon of paint; one will typically buy by the quart. 

How Much Paint Do I Need for the Ceiling?

Calculating how much paint is needed for a ceiling again follows the same equation as above. Since ceilings tend to be open flat spaces with few large obstructions, it is even easier. Just measure the length and width of the ceiling, multiply them together, then divide by 400. 

While a house may have lights or fans, the square footage used is often minimal, so we recommend not worrying about attempting to remove that element from the equation. 

Painting Secrets Every Professional Knows

The more one paints, the more tips and tricks are learned along the way. Here are a few painting secrets that every professional knows by heart.

First, it is better to have too much paint than too little. We always recommend aiming higher to avoid another store trip where you will have to attempt color matching. Plus, having extra in case of spills or for touch-ups down the line is always helpful. Most professionals keep 1-2 quarts of excess paint on hand. 

Second, one must understand the surface they are painting. Stucco and unpainted drywalls are porous surfaces, meaning they will absorb paint at a higher rate. Therefore, more paint will be needed than the average calculation will supply. 

Third, one can get away with a single coat of paint in a few instances. For example, one can do new white paint over clean white paint or paint an identical color on top of an already painted wall well with just a single coat. 

Choose Paintmaster for Your House Painting Professional

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When it comes to house painting projects, it can be overwhelming to take the time and effort to complete all of these calculations in addition to the painting. Rather than adding unnecessary stress and frustration to your life, you can choose to have an experienced and reliable paint professional complete your project for you. Not only will you receive a high-quality performance, but it will be done quickly and efficiently so you can return to enjoying your home. We encourage you to review our residential services to learn more about our interior house painting process.

Request a free house painting estimate today to start your house painting project!

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