Blown-In Insulation Bag Calculator
How many bags of blown-in insulation? Use the coverage-per-bag chart, or the board-feet-by-depth method as a cross-check.
Calculator
1,000 ft² to R-38 takes about 28 bags (coverage-at-R chart), roughly 15.2 inches deep. The coverage-at-R chart and the board-feet yield are two independent labeled manufacturer inputs — use the one printed on YOUR bag, and blow a little deep to allow for settling.
Every bag of loose-fill prints two numbers you can plan from: the square feet it covers at a given R, and the board-feet it yields. This tool runs both. The coverage-per-bag chart is the fast, official way; the board-feet-by-depth method is the independent cross-check that catches a mislabeled bag or a settling surprise. When the two disagree, order to the higher count.
The default blows a 1,000 ft² attic to R-38 with blown fiberglass (~37 ft²/bag at R-38).
Formula
By coverage chart: bags = ceil( area_sqft ÷ coverage_at_R )
By depth (board-feet): depth_in = target_R ÷ R_per_inch, then bags = ceil( area_sqft × depth_in ÷ bag_yield_boardfeet )
Worked example
Coverage chart, 1,000 ft² at R-38. Blown fiberglass covers ~37 ft²/bag at R-38: 1,000 ÷ 37 = 27.0 → 28 bags. At R-49 the same product covers only ~28 ft²/bag: 1,000 ÷ 28 = 35.7 → 36 bags.
Depth method, 1,000 ft² to R-49 in cellulose. Depth = 49 ÷ 3.5 = 14″. Bags = 1,000 × 14 ÷ 450 = 31.1 → 32 bags. Two independent inputs, close agreement — confidence you ordered right.
Background & practice
Coverage collapses as you go deeper. The same bag that covers ~108 ft² at R-13 covers only ~23 ft² at R-60, because you are piling far more material into each square foot. Never reuse a low-R coverage number for a high-R attic.
Settling is real. Loose-fill fluffs at the machine and settles over months, especially fiberglass. Blow to the depth cards, not to the eye, and set the cards a touch over target. Cellulose is often installed at a stated settled density to fight this.
What to measure first: attic floor area (not roof area), the depth cards you will install to, and the coverage chart on the specific bag. Rent-with-purchase blowers are common — buy the bags first so the machine time matches.
Reference table
| Target R (blown fiberglass) | Coverage per bag (labeled) | Bags for 1,000 ft² |
|---|---|---|
| R13 | 108 ft²/bag | 10 bags |
| R19 | 74 ft²/bag | 14 bags |
| R30 | 47 ft²/bag | 22 bags |
| R38 | 37 ft²/bag | 28 bags |
| R49 | 28 ft²/bag | 36 bags |
| R60 | 23 ft²/bag | 44 bags |
Coverage per bag falls as you blow deeper for a higher R. The board-feet method (bag yield ~450 bd-ft) is the independent cross-check — use the chart on YOUR bag.