Attic Insulation Calculator
Estimate added attic-insulation thickness, volume, packages and cost from attic area, current R-value, target R-value and product coverage.
Default project preview
12.4 in
Added R-value
R-36
Base added depth
11.3 in
Packages
289
Installed volume index
17,325 ft²·in
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Input and output guide
What each value means
The labels and units below are part of this calculator’s visible methodology. Replace every default with measurements or product data from the actual project.
Attic area
Enter this project assumption in ft². The current imperial default is 1400 ft².
Current insulation value
Enter this project assumption in R. The current imperial default is 13 R. Minimum: 0.
Planning target
Enter this project assumption in R. The current imperial default is 49 R.
Product value per depth
Enter this project assumption in R per in. The current imperial default is 3.2 R per in.
Package coverage at one depth unit
Enter this project assumption in ft²·in. The current imperial default is 60 ft²·in.
Settlement and access allowance
Enter this project assumption in %. The current imperial default is 10 %. Minimum: 0. Maximum: 40.
Price per package
Enter this project assumption in per package. The current imperial default is 58 per package. Minimum: 0.
How to read the outputs
Added R-value
target minus current value. Default preview: R-36.
Base added depth
before settlement allowance. Default preview: 11.3 in.
Packages
rounded to whole packages. Default preview: 289.
Installed volume index
area × order depth. Default preview: 17,325 ft²·in.
Purchased coverage index
packages × entered coverage. Default preview: 17,340 ft²·in.
Material allowance
packages × entered price. Default preview: $16,762.00.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Added R-value = target − current. Base depth = added R-value ÷ product R per depth unit. Apply settlement allowance. Packages = round up (attic area × order depth ÷ package coverage index).
Reviewed project guidance
How to use this estimate in a real project
Last reviewed: July 30, 2026
Estimate attic insulation area, volume and package count from net floor area, target depth and product coverage.
Calculation steps
- 1Measure the insulated attic floor area.
- 2Subtract only truly uninsulated zones.
- 3Enter target depth or manufacturer coverage for the required R-value.
- 4Round to whole bags or packages.
Worked numerical example
A 1,200 ft² attic requiring 10 in of loose-fill insulation contains 1,000 ft³. If one bag covers 50 ft² at that depth, order 24 bags before project allowance.
Purchasing and rounding
Use the product chart for the exact target R-value and installed density; maintain clearance and ventilation details.
Interpret the result
Package quantity does not confirm code R-value, air sealing or moisture control.
Page-specific assumptions
- Uniform target depth.
- Coverage chart matches product and R-value.
- Settling is handled by manufacturer coverage.
Common mistakes
- Using bag volume instead of coverage chart.
- Insulating before air sealing.
- Blocking soffit ventilation.
Primary and technical references
BuildMeter provides planning estimates, not engineering, architectural, electrical, mechanical, plumbing, permit or code approval. Review the methodology and verify final decisions with product documentation and qualified professionals.
Related tools
Continue planning the project
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Attic Insulation Calculator questions
Why must product coverage be entered at one depth unit?+
Blown and batt products have different package yields. A coverage index lets package quantity scale with the required installed depth.
Should old insulation be removed?+
Not always. Existing insulation condition, contamination, moisture, air leakage and access determine whether it can remain.
Does this choose the correct target R-value?+
No. The target is editable because climate, assembly and local energy requirements vary.