Rolls of fiberglass insulation, also known as batting, come in different lengths, widths and with differing R values. 

Common Insulation Roll Lengths are:

• 18' (R-15),
• 22' (R-30),
• 32' (R-13),
• 39'2" (R-19),
• 40' (R-11). 

Common Insulation Roll Widths are:

• 15", which  fits between 16" spaced studs and joists, and
• 23", which fit in between 24" spaced joists and trusses.