Formula
The face of one batt is 15 times 93 inches, divided by 144:
batts = ceil(area / (15 × 93 / 144))
That face is 9.6875 square feet. The R-value does not change the count. Drywall sheets use 32 or 48 square feet instead.
Assumptions
- Batts are 15 inches wide and 93 inches long.
- They fit 16 inch on-center studs.
- A cut batt is ordered whole.
Worked example
310 square feet of wall needs 32 batts.
Input definitions
- Batt face
- The wall area one piece covers, not the thickness and not the R-value.
Limitations
A 24 inch stud bay uses a wider batt. Ceiling batts can be a different length. The package coverage replaces this face when it is printed.
Questions
Why 93 inches?
It is a standard batt length for an 8 foot wall after the plates are subtracted from a full 96 inches.
Does a higher R-value need more batts?
Not in this count. A thicker batt can have the same face. You still buy the R-value the cavity needs.