Insulation Calculator
Estimate blown-in attic or wall insulation. Enter the area to cover and your target R-value to get the required depth, the number of bags, and an estimated material cost.
Your project
Estimate
Bags needed · Blown-in fiberglass, ≈30 ft³ yield per bag
- Area to cover
- 900ft²
- Required depth
- 15.2in
- Estimated material cost
- $684.00
Estimates are guidance only and exclude tax, labor, and site conditions unless stated. Confirm with a local pro.
How it's calculated
No black boxes — here is the exact math behind your estimate, so you can check it or adapt it for your own quote.
- 1
Required depth (in) = R-value ÷ 2.5 (R-value per inch for blown-in fiberglass) - 2
Volume (ft³) = area × (depth ÷ 12) - 3
Bags = ⌈ volume (ft³) ÷ 30 ⌉ (≈30 ft³ net coverage per bag) - 4
Cost = bags × price per bag
Worked example
A 30 ft × 30 ft attic insulated to R-38.
Inputs
- Area length
- 30 ft
- Area width
- 30 ft
- Target R-value
- 38
- Price per bag
- 18 $/bag
Result
- Bags needed
- 38 bags
- Area to cover
- 900 ft²
- Required depth
- 15.2 in
- Estimated material cost
- $684.00
Tools & materials for this project
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- Insulation rolls Faced batts for walls, ceilings, and floors.
- Blown-in insulation Loose-fill for topping up attic coverage.
Compare local pros for attic insulation
An estimate gets you a budget. A few competing quotes get you the real price. Tell us about the job and we'll help you find vetted contractors nearby.
Insulation cost by state
The calculator does the quantity math exactly. What it can't know is what a fair unit price looks like where you live — attic insulation runs 61% more in the priciest US market than the cheapest.
Insulation cost in all 50 states + DC US average $2.00 per square foot installed · regional averages, full ranked table, and typical project totals.