Insulation Calculator

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For an attic floor, multiply length × width of the space. Split an irregular area into rectangles and add them.
sq ft
Cellulose packs more R per inch (about 3.5) so it needs less depth; loose fiberglass is about 2.5 per inch.
Pick your IECC climate zone to auto-fill the Energy Star attic R-value. Choose "Pick target R-value myself" to override.
If you are adding to insulation already in place, enter its current R-value so only the shortfall is filled. Leave at 0 for a bare cavity.
Open attic blows settle to the rated depth. Walls are dense-packed and use more material per square foot than this open-blow estimate.
Extra for offcuts, gaps trimmed around joists and pipes, and uneven coverage. 10% is typical; use 15% for cut-up, irregular spaces.
%
Advanced: leave at 0 to let the calculator derive coverage. Enter a value only if your bag label states coverage at your exact target R-value.
sq ft/bag
Currency
Bags needed
77 bags of cellulose
Required settled depth14 in
Coverage per bag14.3 sq ft
Installed volume (with waste)1,283.3 ft³
Total material weight1,925 lb
Exact bags (un-rounded)77

Buy 77 bags of cellulose, blown to 14 in settled depth.

  • Depth is set by the R-value you are aiming for: cellulose delivers about 3.5 R per inch, so a higher target means a deeper, heavier layer.
  • Coverage per bag is derived, not guessed: each bag fills a fixed settled volume (16.7 cubic feet), which spreads thinner at low R and thicker at high R.
  • Blown fibre settles after install, so the rated depth above is the settled figure, install a little fluffier so it relaxes to target.

Next stepMark the joists at the target depth before you blow, then sweep the attic to confirm the whole floor reaches that line.

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