Fiberglass batt: R-value per inch
Short answer
Fiberglass batt adds about R-3.1 per inch, so you need roughly 9.7" for R-30 and 15.8" for R-49.
R-value per inch
R-3.1
Best for
Walls, floors, and accessible joist bays
Fiberglass batt thickness chart
| Target R-value | Thickness needed |
|---|---|
| R-13 | 4.2" |
| R-19 | 6.1" |
| R-30 | 9.7" |
| R-38 | 12.3" |
| R-49 | 15.8" |
| R-60 | 19.4" |
How much for your home?
Calculate fiberglass battOther materials
Frequently asked questions
How many inches of fiberglass batt do I need for R-49?
About 15.8" of fiberglass batt, since it adds roughly R-3.1 per inch (R-49 ÷ 3.1).
What is the R-value of fiberglass batt per inch?
Fiberglass batt provides about R-3.1 per inch (a typical value — density and brand vary). So 9.7" gives roughly R-30.
What is fiberglass batt best used for?
Walls, floors, and accessible joist bays. Compare it against other materials for your target R-value in the calculator.