HVAC & Energy
Blown-In Insulation Calculator
Plan loose-fill attic insulation using the selected product's bag coverage row. Compare current and target R-values, round an order to whole bags, or find coverage from bags already available.
Change any input to update the calculation. Unit changes preserve the physical quantity.
Inputs
Effective existing layer only. Use 0 if uncertain; R-values are not insulation depths.
Your local currency; no product price is assumed.
Calculated locally in your browser. No sign-up or input upload.
Results
Whole bags to order
16Coverage / net project area
100 m²1,076.391 ft²Required additional R-value
30 h·ft²·°F/BTU5.283 m²·K/WSelected product-row R-value
30 h·ft²·°F/BTU5.283 m²·K/WEstimated total layer R-value
30 h·ft²·°F/BTU5.283 m²·K/WAdded installed depth
281.94 mm11.1 inAdded settled depth
281.94 mm11.1 inProduct coverage per bag
6.781 m²72.993 ft²Bag material cost
0 local currencyCalculation breakdown
- Coverage row
- Added label R 30 (US) · 72.9927 ft²/bag
- Order method
- Both manufacturer minimum bag density and maximum coverage are respected; whole bags round upward.
Assumptions & checks
Confirm the current bag label before ordering. The named JM attic chart is a reference snapshot; other products, cavity applications and installation methods use different charts.
Existing-plus-added R assumes continuous compatible layers. Moisture, air leakage, bridging, ventilation, clearances and fire requirements need separate assessment.
Formula
No universal R-per-inch or bags-per-area constant is used. A coverage row must meet the required additional R-value; between reference rows the next higher row is selected without interpolation.
Worked example
Using the default values shown in the calculator, the same formula gives the following result. This is a quick sanity check for the calculation, not a design recommendation.
Inputs
- Coverage data
- JM attic reference
- Net area to insulate
- 100 m²
- Assessed existing R-value
- 0 h·ft²·°F/BTU
- Target total R-value
- 30 h·ft²·°F/BTU
- Order allowance
- 5 %
- Price per bag (optional)
- 0
Result
- Whole bags to order
- 16
- Coverage / net project area
- 100 m²
- Required additional R-value
- 30 h·ft²·°F/BTU
- Selected product-row R-value
- 30 h·ft²·°F/BTU
- Estimated total layer R-value
- 30 h·ft²·°F/BTU
- Added installed depth
- 281.94 mm
- Added settled depth
- 281.94 mm
- Product coverage per bag
- 6.781 m²
- Bag material cost
- 0 local currency
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Technical references for this calculation
Frequently asked questions
Can I use any insulation product with the reference chart?
No. Use the current coverage chart for the exact product and application, or select manual label data. Fiberglass, cellulose and cavity-fill coverage are not interchangeable.
How is an in-between R target handled?
The named reference chart selects the next higher listed additional R-value. Manual data must already meet the required added R. No invented linear interpolation of bag coverage is used.
Is this a building-code insulation recommendation?
No. The target R-value is your input. Climate-zone requirements, installation clearances and assembly performance require separate project-specific checks.
Reference data & method sources
- Johns Manville: Climate Pro attic coverage reference
Archived attic chart used as a named reference preset. Confirm the current product bag label; cavity-wall charts and other products are not interchangeable.
Reference tables
Climate Pro attic reference rows
Reference snapshot. Bag count honors both minimum bag density and maximum coverage. Verify the current product label.
| R (US) | Installed in | Settled in | Min bags/1000 ft² | Max ft²/bag |
|---|---|---|---|---|
| 11 | 4.3 | 4.3 | 4.8 | 209 |
| 13 | 5 | 5 | 5.7 | 176 |
| 19 | 7.2 | 7.2 | 8.4 | 118 |
| 22 | 8.3 | 8.3 | 9.9 | 101 |
| 26 | 9.7 | 9.7 | 11.8 | 85 |
| 30 | 11.1 | 11.1 | 13.7 | 73 |
| 38 | 13.8 | 13.8 | 17.7 | 56 |
| 44 | 15.7 | 15.7 | 20.8 | 48 |
| 49 | 17.3 | 17.3 | 23.5 | 43 |
| 60 | 20.7 | 20.7 | 29.5 | 34 |