SmartInsulationCalculator

Blown-In Insulation Calculator

Loose-fill is sold by the bag, and each bag covers less area the deeper you blow it. Enter your area and target R-value to get the bag count, settled depth and cost.

Your project

Covers cuts, compression and odd bays. 10% is the usual default.

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Prices as of Oct 11, 2026, 4:41 AM UTC. Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.

How this calculator works

  • Bags = (target R × area) ÷ bag coverage rating
  • Coverage per bag = bag rating ÷ target R
  • Settled depth = target R ÷ R-per-inch

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Frequently asked questions

Cellulose or blown fiberglass?

Cellulose packs a bit more R per inch and blocks air movement better; fiberglass is lighter, won't absorb water, and won't settle as much. Both perform fine when installed to the depth on the bag.

Do I need to rent a blower?

Yes for anything over a small area. Most big-box stores lend the machine free when you buy enough bags — usually 10 to 20.

How many bags of insulation do I need per square foot?

It depends on the R-value you are aiming for, not on the area alone. Manufacturers publish coverage as an R-value at a given square footage per bag, so the same bag covers roughly half as much area at R-60 as at R-30, because you are laying it twice as deep. The calculator takes your target R-value and area and returns the bag count directly.

Cellulose or fibreglass for blown-in?

Cellulose has a higher R per inch, so it reaches a target in less depth, and it packs more densely which slows air movement through it. Blown fibreglass is lighter, which matters on a ceiling with marginal framing, and it does not absorb water in the way cellulose does. Both are established; the choice usually comes down to depth available and local price.

Does blown-in insulation settle?

Yes, and the published coverage figures already account for it — manufacturers rate bags at settled thickness rather than the depth it looks immediately after blowing. This is why you should install to the marked depth and expect it to drop, rather than installing to the final depth and finding yourself short once it settles.

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Bags required

108 bags

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