Insulation R-Value Calculator
Find the recommended attic insulation R-value for your climate zone and how many inches of fiberglass, cellulose or spray foam it takes to get there.
How to use
- 1Choose your US climate zone and the insulation type.
- 2Enter the R-value (or inches) you already have to see how much to add.
How it's calculated
Inches needed = (target R − existing R) ÷ R per inch. Typical R per inch: fiberglass batts 3.2, blown fiberglass 2.5, blown cellulose 3.5, open-cell spray foam 3.6, closed-cell spray foam 6.5.
Frequently asked questions
What R-value should my attic have?
ENERGY STAR recommends about R-30 to R-49 in the warmest zones and R-49 to R-60 in most of the US.
What is R-value?
Resistance to heat flow — higher is better. R-values of layers add together.
Should I seal air leaks first?
Yes — air sealing around lights, pipes and attic hatches often saves as much energy as the extra insulation.