How many bags of blown-in insulation do you need?
Measure the net area and use the maximum coverage per bag from the actual product chart at your chosen R-value. Bag quantity is rounded up. This loose-fill method differs from dividing batt or rigid-board coverage across a surface.
Blow in insulation uses this same bag takeoff. Coverage must match the manufacturer’s installed or settled thickness and stated target R-value; bag weight alone does not determine insulation coverage.
Which information must come from the coverage chart?
Copy the same chart row’s chosen R-value, maximum area per bag, minimum initial thickness and, where provided, minimum settled thickness. Mass-check mode also requires minimum installed mass per area and net bag mass. Do not combine entries from different R-value rows.
| Input | Units |
|---|---|
| Attic / surface length | ft / m |
| Attic / surface width | ft / m |
| Excluded area (optional) | ft² / m² |
| Maximum label coverage per bag at chosen R-value | ft² / m² |
| Minimum initial installed depth from label | in / cm |
| Minimum settled depth from label (optional) | in / cm |
| Chosen product-chart R-value (US units) | as labeled |
| Existing effective R-value (optional) | as labeled |
| Project target total R-value (optional) | as labeled |
| Minimum label mass per area (kg/m², optional) | as labeled |
| Net bag mass (kg) | as labeled |
| Bag allowance (%) (optional) | as labeled |
| Price per bag (optional) | as labeled |
How are coverage and minimum-mass requirements checked?
Coverage bags equal net area divided by maximum coverage per bag, rounded up. Mass bags equal net area times required mass per area divided by bag mass, rounded up. In mass-check mode the larger count governs, before an optional order allowance.
Coverage bags = ceil(net area ÷ label coverage per bag); mass bags = ceil(net area × label minimum mass per area ÷ bag mass); use the larger requirement
What does a thousand-square-foot attic require?
With illustrative label coverage of 50 sq ft per bag, 1,000 sq ft needs 20 bags before allowance. This arithmetic does not certify an R-value. The product row’s minimum installed thickness and applicable mass requirement must also be satisfied.
Can you use a metric product coverage chart?
Dimension and coverage fields switch between feet and meters or square feet and square meters. Thickness switches between inches and centimeters. Required mass per area stays kg/m² and bag mass stays kg. The R-value fields use US R units; RSI needs a separate conversion.
Why are installed depth and settled depth separate?
Some loose-fill products settle after installation. A product chart can distinguish initial and settled thickness requirements. The worksheet displays both supplied depths and rejects a settled depth greater than the initial depth; it does not infer settlement or R-value from thickness alone.
How is existing insulation reflected in a target check?
The optional nominal comparison adds supplied existing effective R-value to the chosen chart R-value. This is an idealized layered comparison. Compression, gaps, thermal bridges and uncertain existing material performance can reduce whole-assembly effectiveness.
What does a bag allowance change?
It increases the order count after the governing minimum bags have been calculated. It does not lower a minimum installation depth or replace a density requirement. Product price multiplies the final whole-bag order, keeping spare quantity distinct from the minimum coverage count.
How do you compare products or R-value rows?
Save one complete product row, then enter another product’s matched coverage, depths and mass values. Compare governing bags and cost. A larger bag mass does not automatically mean larger coverage at the same R-value; the manufacturer’s chart determines the relationship.
Which insulation calculator applies to batts and boards?
Use the Insulation Calculator for batt, roll or rigid-board package coverage. Use the Heating BTU Calculator only after the assembly U-values have been established.
