Blown-in fiberglass: R-value per inch
Short answer
Blown-in fiberglass adds about R-2.5 per inch, so you need roughly 12.0" for R-30 and 19.6" for R-49.
R-value per inch
R-2.5
Best for
Attics (most common attic material)
Blown-in fiberglass thickness chart
| Target R-value | Thickness needed |
|---|---|
| R-13 | 5.2" |
| R-19 | 7.6" |
| R-30 | 12.0" |
| R-38 | 15.2" |
| R-49 | 19.6" |
| R-60 | 24.0" |
How much for your home?
Calculate blown-in fiberglassOther materials
Frequently asked questions
How many inches of blown-in fiberglass do I need for R-49?
About 19.6" of blown-in fiberglass, since it adds roughly R-2.5 per inch (R-49 ÷ 2.5).
What is the R-value of blown-in fiberglass per inch?
Blown-in fiberglass provides about R-2.5 per inch (a typical value — density and brand vary). So 12.0" gives roughly R-30.
What is blown-in fiberglass best used for?
Attics (most common attic material). Compare it against other materials for your target R-value in the calculator.