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Blown-In Insulation Calculator
Your attic
Typical US coverage and prices — not a quote. Always check the coverage chart printed on the bag you buy: coverage varies by brand, and the chart is the final word for your job.
Example: 1,000 sq ft at R-49 with cellulose (21 sq ft per bag, $14 per bag) → 53 bags with 10% waste, $742 of material, about 13.2 inches deep.
Behind the numbers
How blown-in insulation is calculated
One bag of loose-fill insulation covers a fixed area at a given R-value: the deeper you blow it, the less area each bag covers. The coverage per bag comes from the manufacturer's chart, and this calculator uses typical US figures for each material and R-value. Bags are the area divided by the coverage per bag, plus a waste allowance (10% is a common figure) for settling and uneven spots, rounded up — you cannot buy part of a bag. Depth is the R-value divided by the material's R-value per inch. Material cost is bags times the typical bag price.
Worked example: 1,000 sq ft at R-49 with cellulose, coverage 21 sq ft per bag: 1,000 ÷ 21 = 47.6 bags, × 1.10 waste = 52.4, rounded up to 53 bags. Material cost: 53 × $14 = $742. Depth: 49 ÷ 3.7 = 13.2 inches.
Reference
Coverage per bag by material and R-value
| R-value | Cellulose (sq ft / bag) | Fiberglass (sq ft / bag) | Mineral wool (sq ft / bag) | Depth, cellulose |
|---|---|---|---|---|
| R-13 | 80 | 95 | 72 | 3.5 in |
| R-19 | 52 | 65 | 48 | 5.1 in |
| R-30 | 34 | 45 | 31 | 8.1 in |
| R-38 | 27 | 36 | 25 | 10.3 in |
| R-49 | 21 | 28 | 19 | 13.2 in |
| R-60 | 17 | 23 | 15 | 16.2 in |
Typical US coverage from manufacturer charts: cellulose about R-3.7 per inch, fiberglass about R-2.5 per inch, mineral wool about R-3.1 per inch. Bag prices used here: cellulose $14, fiberglass $19, mineral wool $36. Depths shown are for cellulose; fiberglass runs deeper and mineral wool sits between the two.
Worked examples
Example insulation jobs
| Job | Material | Bags (incl. 10% waste) | Depth | Material cost |
|---|---|---|---|---|
| 1,000 sq ft, R-49 | Cellulose | 53 | 13.2 in | $742 |
| 1,200 sq ft, R-38 | Fiberglass | 37 | 15.2 in | $703 |
| 1,000 sq ft, R-30 | Mineral wool | 36 | 9.7 in | $1,296 |
| 800 sq ft, R-19 | Cellulose | 17 | 5.1 in | $238 |
Tips before you buy
Read the chart on the bag, not just this calculator: brands differ, and the chart's coverage for your exact R-value is what the store will honor.
Air-seal the attic floor first — gaps around lights, pipes and wires let warm air escape no matter how thick the insulation is.
Do not block soffit vents: keep baffles in place so air can still flow from the eaves to the ridge.
Cellulose settles over time, which is why the 10% waste allowance matters; measure the depth after a few weeks and top up if it has dropped.
Good to know
Frequently asked questions
How many bags of blown-in insulation do I need?
Divide your area in square feet by the coverage per bag at your target R-value, then add about 10% for waste. For example, 1,000 sq ft at R-49 with cellulose at 21 sq ft per bag needs 1,000 / 21 = 47.6 bags, plus 10% waste = 53 bags.
What R-value should my attic have?
Most US attics aim for R-38 to R-60, depending on the climate zone: R-38 to R-49 in warm zones and R-49 to R-60 in cold zones. Check your local building code, and always read the coverage chart printed on the bag you buy, because coverage varies by brand.
How deep should blown-in insulation be?
Depth is the R-value divided by the material's R-value per inch. Cellulose is about R-3.7 per inch, so R-49 needs about 13.2 inches; blown fiberglass is about R-2.5 per inch, so R-49 needs about 19.6 inches; mineral wool is about R-3.1 per inch, so R-49 needs about 15.8 inches.
How much does blown-in insulation cost?
Material cost is bags times the typical bag price: about $14 a bag for cellulose, $19 for blown fiberglass and $36 for mineral wool in the US. A 1,000 sq ft attic at R-49 with cellulose needs 53 bags, so about $742 of material. That is a material estimate, not a quote — installed prices add labor.