Spike's Calculators

Interior Finishing

Insulating an Attic Using Blown Insulation

As the title indicates, this insulation is blown into the space that needs to be insulated. You can do it without blowing equipment but at a much lower coverage rate per bag. Some places that sell blown insulation will include a free equipment rental with a certain minimum amount of bags. But even if you have to pay for the Insulation Blower rental, the cost is more than likely recovered by the more extensive coverage per bag.

To estimate this product, you will need to know how much one bag covers (cubic foot value), the R-value of the material per 1 inch of coverage (settled), your total required R-value and the square footage of the area.

On the packaging, there will be a coverage chart showing the minimum applied and settled thickness required to meet the "Thermal Resistance," the required R-value. (average value = R 3.6 per inch). Area coverage values per bag are dependent on the package size.

Example Calculation
Length = 10 ft--width = 6 feet--bag coverage= 16.5 cubic ft--R value per 1" = 3.6--required R val. = 12
Area = 10 * 6 = 60 square ft
Required depth to achieve R value needed = R 12 / R 3.6 = 3.3 inches
Volume needed = 60sq ft * 0.275 (3.3 /12 converting to decimal ft) = 16.5 cubic feet
You would need one bag in this case.

Note: The cost is based on rounding up the number of bags needed. In some of the calculations, this will be a very small amount, and you should be able to make do with one less bag.

Attic/Ceiling Insulation-Blown/Plus Cost

Length ft in
Width ft in
Coverage/Volume per Bag ft ³
Stated R value per one inch of depth in
Required R value #
Price of One Bag $


Square Footage of Area ft²
Applied Depth of Insulation in in
Settled Depth in in
Volume of Insulation Needed ft³
Bags Needed #
Cost of Insulation >$

The Calculation

  1. the length of the area (feet + inches)
  2. the width of the area (feet + inches)
  3. the coverage of one bag (cubic feet)
  4. the R value per one inch of thickness of the insulation (settled)
  5. the desired R value
  6. the cost of one bag


  1. the square footage of the area
  2. applied depth of insulation (the height of placing the insulation before it settles)
  3. required depth of insulation (settled)
  4. volume of required insulation (in cubic feet)
  5. number of bags needed (# whole plus partial bags)
  6. cost of the material (based on whole bags needed)

If you have any questions or comments please Contact Us
Privacy Policy
© 1998, VmNet.