What is a board foot?

Spray foam insulation is measured in board feet and we understand that can be a confusing term. It's an old lumber industry term and is still commonly used on production and wholesale side of the timber & lumber industry. We use it in the spray foam industry to communicate total volume of insulation being sprayed.

Understanding how to measure a board foot is useful because it will help you accurately know just how much space you will be insulating, estimate spray foam costs, and more confidently discuss your project with your contractor. 

Board feet are calculated from the square footage of the cavities in the area you are going to insulate.

A board foot is 12 inches by 12 inches by 1 inch.  It's a term from the lumber industry.  Board feet is a measurement of volume and, in this case, is used to find out how much spray foam is needed to fill a space (or how much was used). 


The volume of one board foot is 144 cubic inches. That is important to understand because it helps you understand the board foot equation.

Board Foot Equation

board feet equation with all inches used

If all your measurements are in inches, divide by 144 to calculate board feet.

Tip: Pick one version of the board feet equation and use it consistently.

You just need to remember to convert your measurements to feet or inches accordingly.

Board feet equation with two feet and one inche measurements

You don't need to divide by anything if two of your values are in feet and the other is in inches.

4G Smooth spray foam


Lapolla has over 30 years of expertise helping home and building owners cut their energy bills.

Contact us today for a free insulation quote.

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