Batt Insulation R-Value Per Inch + R11-R49 Thickness Chart

All bat insulations have relatively high R insulation values. In general, we can say that bat insulation R-value ranged between R-3 to R-4 per inch. There is a bit of variety between fiberglass, mineral wool, cotton, and cellulose bats, and we are going to cover all of them.

Namely, with batt insulation, we get these two kinds of questions:

  1. “What is batt insulation R-value per inch?”. Example: If we live in colder climates, we would need R-60 attic insulation, according to this attic R-value insulation chart. By knowing batt insulation R-value per inch, we can calculate the batt insulation thickness we need for up to R-60 attic insulation.
  2. “What is R-30 batt insulation thickness, what is R-38 batt insulation thickness, etc.?”. On batt insulation labels, we can see insulation R-values, including R-11, R-13, R-19, R-25, R-30, R-38, R-44, R-45, and R-49. For insulation planning, knowing how thick these batts are is quite essential.
r 30 fiberglass batt thickness
Laying out R-30 fiberglass batts. The thickness of these R-30 fiberglass batts is 10.25 inches.

We have 4 main types of pre-cut batt insulation materials; fiberglass batts, mineral wool batts, cotton batts, and cellulose bats. To be more precise and type-specific than “batt insulation has R-3 to R-4 per inch values”, we have prepared these two charts that will help you out with planning out your batt insulation:

  1. Batt Insulation R-Value Per Inch Chart (+ 2, 4, 8 Inch Thickness). In this 1st chart, we list R insulation values per inch for all 4 batt types. On top of that, we have also calculated the R-value for 2-inch, 4-inch, and 8-inch thick batts. Example: Fiberglass batts have R-2.9 to R-3.9 per inch insulation. That’s R-5.8 to R-7.8 for 2-inch thickness, R-11.6 to R-15.6 for 4-inch thickness, and R-23.2 to R-31.2 for 8-inch thickness.
  2. Batt Insulation Thickness Chart. In the 2nd chart (which might even be more useful), we list the commercially available fiberglass batt and mineral wool batt thicknesses for R-11, R-13, R-19, R-25, R-30, R-38, R-44, R-45, and R-49 insulation values. Example: For R-38 insulation value, we use 12.25-inch fiberglass batt or 10.25-inch mineral wool batt.

Alright, let’s first have a look at the batt insulation R-value per inch (1st chart), and then check the batt insulation thickness for specific R values (2nd chart):

Batt R-Value Per Inch (2, 4, 8 Inches)

Type Of Batt Insulation: R-Value Per Inch: 2 Inch R-Value: 4 Inch R-Value: 8 Inch R-Value:
Fiberglass Batt R-2.9 To R-3.9 R-5.8 To R-7.8 R-11.6 To R-15.6 R-23.2 To R-31.2
Mineral Wool Batt: R-3.1 To R-4.3 R-6.2 To R-8.6 R-12.4 To R-17.2 R-24.8 To R-34.4
Cotton Batt: R-3.0 To R-3.7 R-6.0 To R-7.4 R-12.0 To R-14.8 R-24.0 To R-29.6
Cellulose Batt: R-3.2 To R-3.8 R-6.4 To R-7.6 R-12.8 To R-15.2 R-25.6 To R-30.4

As we can see from this 1st chart, the premise “batt insulation values range from R-3 to R-4” is quite in line with the actual R-values. Some of the lowest quality fiberglass batts can be below R-3 per inch (R-2.9, to be specific), and mineral wool batts can reach R-4.3 per inch insulation values.

Which batt has the highest R-value?

Just looking at the R values of these 4 types of batts, you can see that mineral wool and cellulose batts have, on average, a bit higher R-value per inch (up to R-4.3) than fiberglass and cotton batts (up to R-3.8). That’s why commercially available mineral wool batts don’t need to be as thick as fiberglass batts for the same R-value (more about that in the 2nd chart).

The difference at 1-inch R values are not all that substantial. However, when you check the 2-inch, 4-inch, and especially 8-inch batt thicknesses, we can see that the difference between “bad” fiberglass batt and “good” mineral wool batt can be over R-10 (R-11.2 difference for 8-inch batts, to be exact).

Let’s now look at the thickness of fiberglass and mineral wool batts ranging from R-11 to R-49 in this next chart:

Batt Insulation Thickness Chart

R Insulation Value: Batt Thickness (Inches):
R-11 3.5 Inch Fiberglass Batt
R-13 3.5 Inch Mineral Wool Batt
R-19 6.25 Inch Fiberglass Bat
R-23 6.25 Inch Mineral Wool Batt
R-25 8.25 Inch Fiberglass Batt
R-30 10.25 Inch Fiberglass Batt or 8.25 Inch Mineral Wool Batt
R-38 12.25 Inch Fiberglass Batt or 10.25 Inch Mineral Wool Batt
R-44 14 Inch Fiberglass Batt
R-45 12.25 Inch Mineral Wool Batt
R-49 14 Inch Mineral Wool Batt

Here, the difference between standard R-value fiberglass and mineral wool batts is very obvious. Here are the batt thickness that corresponds to specific R insulation values:

  • For R-11 insulation, you need a 3.5-inch fiberglass batt.
  • For R-13 insulation, you need a 3.5-inch mineral wool batt.
  • For R-19 insulation, you need a 6.25-inch fiberglass batt.
  • For R-23 insulation, you need a 6.25-inch mineral wool batt.
  • For R-25 insulation, you need an 8.25-inch fiberglass batt.
  • For R-30 insulation, you need a 10.25-inch fiberglass batt or an 8.25-inch mineral wool batt.
  • For R-38 insulation, you need a 12.25-inch fiberglass batt or a 10.25-inch mineral wool batt.
  • For R-44 insulation, you need a 14-inch fiberglass batt.
  • For R-45 insulation, you need a 12.25-inch mineral wool batt.
  • For R-49 insulation, you need a 14-inch mineral wool batt.

You can see the difference in fiberglass vs. mineral wool batt thicknesses for the most common R-30 and R-38 batts in 2 inches in favor of thinner mineral wool batt. Example: For R-30, we have a 10.25-inch fiberglass batt vs. an 8.25-inch mineral wool batt.

You can also notice that for the highest R-values, we generally use mineral wool batts (12.25-inch thick batts for R-45 insulation and 14-inch batts for R-49 insulation).

We hope that you can find everything you need regarding the batt insulation R-values in these 2 charts. If you have any questions, additions, or suggestions, you can use the comment section below. Thank you.

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