R-value determines coverage
The higher the R-value (insulating power) you're targeting, the more material each bag or roll covers — so a bag might cover 60 ft² at R-30 but only 40 ft² at R-49. That's why we ask for the coverage printed on the package rather than guessing. Attics typically aim for R-49 to R-60; walls for R-13 to R-21. Don't compress batts, and keep vents clear.