Blown-In Insulation Calculator
Estimate blown-in insulation bags from area and target depth.
Project details
Enter your measurements below.
The coverage chart on the bag matters more than a generic bags-per-attic rule
Blown-in insulation is unusual because installed thermal performance depends on product-specific depth, density and minimum bag count. Two products with the same bag weight can have different coverage. This calculator helps scale a manufacturer coverage reference to the area and target depth you enter, but the product's official chart remains the controlling source for R-value and minimum-bag requirements. Do not treat the result as a substitute for the chart or for air-sealing, ventilation and clearance work.
Bag coverage and installed depth are product-specific.
R-value is not determined by depth alone across different products.
Air sealing, ventilation baffles and heat-source clearances are separate requirements.
How to use the Blown-In Insulation Calculator
- Measure the insulated horizontal area, excluding sections that will not receive blown insulation.
- Choose the target thermal assembly and obtain the exact manufacturer's depth/coverage or minimum-bag chart.
- Enter a reference coverage/depth consistent with that chart and calculate the whole-bag quantity for the measured area.
- Compare the result back to the official minimum bag count and installed-depth requirements before purchasing.
Why bag count and depth must be checked together
An installer can hit a visible depth with too little material if the installed density is low. Manufacturer charts often specify both minimum bags per area and minimum settled/installed thickness.
Use the result as a cross-check
Plan bag delivery and handling with DIYGauge, then verify that the selected product chart yields the intended assembly performance.
Worked example: 1,000 sq ft attic
- Area
- 1,000 sq ft
- Target
- Chosen from product chart
- Coverage reference
- Manufacturer-specific
- Bag count
- Calculated then compared with chart minimum
The calculator can scale the bag requirement to 1,000 sq ft, but the final accepted count must still meet the manufacturer's stated bags-per-area and depth for the chosen thermal target.
Practical planning tips
Use net insulated area, but do not cover required ventilation paths, access clearances or heat-producing equipment zones.
Record the exact product name with the coverage assumptions; switching cellulose or fiberglass products can invalidate the bag count.
Air sealing is most effective before insulation is added and should not be confused with simply increasing depth.
Mark depth gauges as required by the installation method so finished depth can be checked across the space.
Common mistakes to avoid
Using a generic density/coverage from a different insulation product.
Choosing depth from a desired R-value without checking the manufacturer's product-specific chart.
Ignoring minimum bag count because the visible surface reaches the target depth.
Filling ventilation or safety clearance zones to make the area calculation easier.
Blown-In Insulation Calculator FAQs
How many bags of blown insulation do I need?+
Use the manufacturer's coverage/minimum-bag chart for the exact product, scaled to your measured area and target assembly.
Can I calculate R-value from depth alone?+
Not reliably across different products. Thermal performance depends on the product and installed density; use the product chart.
Why does the calculator need a coverage reference?+
Because one bag's effective coverage changes with target depth and product characteristics.
Does this include air sealing and ventilation work?+
No. Those are important building-envelope tasks but are separate from insulation bag quantity.