R-13 thickness by insulation type
| Material | Typical R per inch | Thickness for R-13 |
|---|---|---|
| Blown fiberglass | R-2.5 | 5.2 in |
| Blown cellulose | R-3.5 | 3.7 in |
| Fiberglass batts | R-3.2 | 4.1 in |
| Mineral wool batts | R-3.3 | 3.9 in |
| Open-cell spray foam | R-3.6 | 3.6 in |
| Closed-cell spray foam | R-6.5 | 2 in |
R-13 is typical for 2×4 or 2×6 walls and floors over unheated spaces. These depths use typical R-per-inch values; the label or bag chart for your product gives the exact settled thickness.
How much material for 1,000 sq ft at R-13?
Blown fiberglass at 5.2 inches over 1,000 sq ft is about 433 cubic feet of installed insulation; cellulose at 3.7 inches is about 310 cubic feet. Bag coverage varies by product, so enter the coverage from the bag chart in the calculator above to get an exact bag count.
The math
R-13 ÷ R-2.5 per inch = 5.2 in (blown fiberglass)
R-13 ÷ R-3.5 per inch = 3.71 in (blown cellulose)
Common questions
How thick is R-13 blown-in insulation?
About 5.2 inches of blown fiberglass or 3.7 inches of blown cellulose.
How thick is R-13 batt insulation?
About 4.1 inches for standard fiberglass batts (R-3.2 per inch); high-density batts are thinner.
Want the full method, tips and other sizes? See the insulation calculator guide.