Insulation R-Value Calculator
Estimate combined insulation R-value, framing-adjusted effective R-value, U-factor, package quantity, heat flow and material cost.
Default project preview
20.61 R
New insulation value
19.25
U-factor
0.0485
Estimated heat flow
1,455 BTU/h
Coverage order
1,100 ft²
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Nominal R-value = existing R + insulation value per thickness × thickness × layers. Effective R applies the entered thermal-bridging reduction. U-factor = 1 ÷ effective R.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Insulation R-Value Calculator questions
Can R-values be added directly?+
Layer R-values can usually be added in a simple one-dimensional path, but framing and other bridges reduce whole-assembly performance.
Why is effective R-value lower than nominal?+
Studs, joists, fasteners and gaps conduct more heat than the insulation, reducing average assembly resistance.
Does more insulation always produce the same savings?+
No. Each added increment provides diminishing heat-flow reduction, and air sealing can be equally important.