Insulation Calculator
Example: Area to insulate: 1000 sq ft · Coverage per bag or bundle: 40 sq ft · Price per bag or bundle: 45 $ · Waste allowance: 5 %
| Bags or bundles to buy | 27 |
| Total material cost | $1,215 |
| Area including waste | 1,050 |
Worked example
To insulate 1,000 square feet with a product covering 40 square feet per bag, and a 5% waste allowance, the padded area is 1,050 square feet. Divide by 40 and round up: 27 bags. At $45 a bag that is $1,215. The higher the R-value you target, the fewer square feet each bag covers, which is why the coverage input, not just the area, drives the count.
Frequently asked questions
What R-value do I need?
Recommended R-values depend on your climate zone and where you are insulating, with attics generally needing more than walls. The U.S. Department of Energy publishes zone-by-zone targets. A higher R-value means thicker insulation and fewer square feet of coverage per bag, so pick the target first.
How is batt insulation coverage listed?
Batt and roll packaging states the square feet each bundle covers for a given cavity depth and R-value. Blown-in insulation lists the coverage per bag at a target R-value on the label as a maximum coverage chart. Read that number off the bag and enter it here.
Why add a waste allowance?
Batts get trimmed around wiring, boxes, and odd bays, and blown-in settles and overfills at the edges, so a small 5 to 10% cushion keeps you from coming up short on the last bay. Tight, obstruction-heavy spaces waste more than open attic floors.
Does more insulation always save money?
There are diminishing returns: going from little insulation to code level saves a lot, while pushing well beyond code saves less per added inch. The Department of Energy's zone recommendations aim at the economically sensible level, so match those rather than simply maximizing R-value.