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R-49 is the common target for the roof or ceiling in cold and mixed climates. That is about 20 inches of blown fibreglass, 15 inches of blown cellulose, 16 inches of fibreglass batt or about 8 inches of closed-cell spray foam. Air seal the ceiling plane before adding any of it.
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.
With these inputs:
| Result | Value |
|---|---|
| Bags required | 108 bags |
| Coverage per bag | 12.2 sq ft at R-49 |
| Settled depth | 13.6 in |
| Estimated material cost | $1,728 |
| Blower rental (1 day) | $110 |
| Pro installed estimate | $2,223 |
Bags = (target R × area) ÷ bag coverage rating · Coverage per bag = bag rating ÷ target R · Settled depth = target R ÷ R-per-inch
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.
Yes for anything over a small area. Most big-box stores lend the machine free when you buy enough bags — usually 10 to 20.
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 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.
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.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.