How to Measure for Floor Insulation Square Footage

Measure the area of your room before buying insulation.

The key to keeping the interior of your home warm during the cool autumn nights and bitter winter days is proper insulation. Waking up and putting your bare feet on an ice cold floor does not make it any easier to get out of bed and ready to start your day. Before installing insulation beneath your floor, you need to know how much to purchase. Measure the area of the room, in square feet, to determine how much insulation to buy.

Things You'll Need

• Tape measure
• Calculator

Instructions

1. Measure the width, which is the shortest side, of the room. Write the number down in feet. Assume the room measures 12 feet wide as an example.

2. Measure the length of the room. Write the measurement down in feet. For example, imagine the room is 16 feet long.

3. Multiply the two numbers together to get the total square footage of the room. Using the example, 12 times 16 is equal to 192 square feet.

4. Measure the largest square or rectangle in the room if the room has odd proportions. Assume a room measures 10 feet long by 5 feet wide in its largest section, but has a smaller alcove that juts out 2 feet by 3 feet. Calculate the largest area by multiplying 5 by 10, for a total of 50 square feet. Calculate the area of the alcove, 2 times 3, for 6 square feet. Add the two numbers together for a total of 56 square feet. Repeat for each section of the room. If it can't be broken down into squares, try to break it down into triangles as well. To calculate that, measure the base times the height divided by 2.

5. Take a measurement of the distance between each of the floor joists to know the width of the insulation you need to purchase.

6. Complete your measuring by determining how deep the floor joists are so you know the thickness of the insulation needed.The insulation does not have to be as thick as the joists, but thicker insulation is better to keep the floor warmer. Measuring the joists gives you the maximum possible thickness to use.

Tips & Warnings

• If your room has odd measurements that can't be figured with rectangles and triangles, estimate the measurement and err on the side of caution and buy slightly more than needed.

• Insulation is rated by R-value, which determines the maximum thickness of insulation you can use for your floor.

• The R-value per inch for fiberglass is from 2.9 to 3.8, while 3.0 to 3.7 is the value for recycled denim.

References

• JohnsManville Home Owner: Crawl Space Insulation
• DIY Home Insulation: How Much Floor Insulation Do I Need?