How to Figure for Bundles of Blown Insulation

Properly insulating your house provides significant savings on your annual energy bill. You can also save money buying the right amount of insulation on the first trip to the hardware store by estimating the number of compressed bundles you'll need for the job. The compression factors for blown-in insulation vary with manufacturers. It's a good idea to visit the hardware store where you'll purchase your material beforehand to get accurate data for your calculation.


Determine the square footage of the area where the insulation is to be installed. Measure the length and width of the area. Multiply these to numbers to get the total square footage.


Consult the product data sheet for the brand of insulation purchased to determine the number of bags per 1,000 square feet required for the target R-value. R-value is a measurement used to designate the amount of thermal resistance provided by the insulation. The higher the R-value, the more thermal protection provided.


Calculate the number of bags required for your application. The standard calculation given by manufacturers for blown insulation is the number of bags per 1,000 square feet required to achieve a desired R-value. Depending on the manufacturer, this number ranges from around 12 to 15 bags per 1,000 square feet for an R-value of 26. For example, the calculation for a space with a desired R-value of 26 measuring 54 feet by 34 feet would look like this:

54 x 34 = 1,836 square feet

With a product requiring 12.8 bags per 1,000 square feet, convert the square footage to a decimal fraction of 1,000. In this case, divide 1,836 by 1,000 for an answer of 1.836. Multiply this by the required number of bags per 1,000 square feet. In this case, the calculation is:

12.8 x 1.84 = 23.5 bags of insulation


Round your answer up to the closest whole number. In the example, 23.5 would be rounded up to 24, so you would need to buy 24 bags of insulation.