Insulation Calculator (R-Value, Thickness and Bags)
Enter area and target R-value to get thickness and quantity.
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Insulation Calculator (R-Value, Thickness and Bags) by TheCalcTools
How the Insulation Calculator (R-Value, Thickness and Bags) works
Pick the insulation type, which sets its R-value per inch.
Thickness = target R ÷ R per inch. Volume = area × thickness.
Batt rolls are area ÷ roll coverage. Blown-in bags are volume ÷ installed volume per bag.
The formula
Worked example
Using the default values shown in the calculator:
| Area to insulate (sq ft) | 1000 |
|---|---|
| Target R-value | 38 |
| Insulation type | Fiberglass batt (R-3.2 per inch) |
| Coverage per batt roll (sq ft) | 40 |
| Installed volume per blown-in bag (cu ft) | 40 |
| Waste | 5 % |
- R-38 with batts at R-3.2 per inch needs 11.9 inches.
- For 1,000 sq ft that is 990 cu ft: 27 rolls of batts or 26 blown-in bags.
Result:
| Thickness needed (in) | 11.9 |
|---|---|
| Insulation volume (cu ft) | 990 |
| Batt rolls (if batts) | 27 |
| Blown-in bags (if blown) | 26 |
| R-value at that thickness | 38.0 |
Frequently asked questions
What R-value do I need in the attic?
It depends on your climate zone. The U.S. Department of Energy publishes recommended levels from about R-30 to R-60 for attics.
Do R-values add up?
Yes. The R-values of layers add together, so you can stack batts to reach a target.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.