Blown-In Insulation Calculator
Bags of blown-in attic insulation needed.
Enter your values
Enter the attic area in sq ft.
Enter the target r-value you are working with.
Enter the r-value per inch you are working with.
Enter the bag coverage in sq ft per bag at 13.5 in.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Bags needed
- 47
- Required blown depth
- 18.1 in
- Coverage per bag at this depth
- 26 sq ft
Quick answer
Bag count comes from the attic area, the target R-value and the bag's coverage chart rate per inch of depth.
bags = ceil(area x depth / coverage per bag at that depth)
At a glance
| What it does | Bags of blown-in attic insulation needed. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Attic area, Target R-value, R-value per inch, Bag coverage |
| Main output | Bags needed |
| Formula | bags = ceil(area x depth / coverage per bag at that depth) |
| Cost | Free — no sign-up, no download |
How to use the Blown-In Insulation Calculator
- 1Enter the attic area and your target R-value for your climate zone.
- 2Use the R-value per inch from the bag's coverage chart.
- 3The calculator adjusts bag coverage for the actual depth you need.
Inputs explained
- Attic area(sq ft)
- Enter the attic area in sq ft.
- Target R-value
- Enter the target r-value you are working with.
- R-value per inch
- Enter the r-value per inch you are working with.
- Bag coverage(sq ft per bag at 13.5 in)
- Enter the bag coverage in sq ft per bag at 13.5 in.
Worked example
Using the values the calculator loads with:
Inputs
- Attic area1200 sq ft
- Target R-value49
- R-value per inch2.7
- Bag coverage35 sq ft per bag at 13.5 in
Results
- Bags needed47
- Required blown depth18.1 in
- Coverage per bag at this depth26 sq ft
Frequently asked questions
What R-value does my attic need?
Cold climates often target R-49 to R-60, milder climates R-30 to R-38 — check local energy code.
Fiberglass or cellulose?
Cellulose is denser and settles more, so check the bag chart depth for your specific product.
What do I need to enter into the Blown-In Insulation Calculator?
Just 4 values: attic area, target r-value, r-value per inch, bag coverage. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Blown-In Insulation Calculator work out the answer?
Bag count comes from the attic area, the target R-value and the bag's coverage chart rate per inch of depth. It applies the formula bags = ceil(area x depth / coverage per bag at that depth) and shows the working so you can check each step by hand.
Is the Blown-In Insulation Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.