Insulation Calculator
How many batt packs of insulation you need
Insulating walls or a ceiling? Enter the area to estimate how many packs of batt insulation to buy.
How much insulation?
Batt insulation is sold by the pack, each covering a stated square footage — commonly around 40 ft². Match the batt width to your stud or joist spacing (16" or 24" on center) and check the R-value for your climate.
Understanding R-value
R-value measures resistance to heat flow — higher is warmer. Walls commonly target R-13 to R-21 and attics R-38 to R-60, but the right number depends on your climate zone (the U.S. DOE publishes recommendations by region). A given wall cavity only fits so much, so higher R-values often mean denser batts or 2×6 framing.
Batts, rolls or blown-in
Pre-cut batts are easiest for open stud and joist bays; rolls suit long runs; blown-in loose-fill is best for attics and existing closed walls. Fit batts snugly without compressing them — gaps and squashed spots are where most heat sneaks through.
Insulation Calculator: frequently asked questions
How do I know how much insulation to buy?
Calculate the wall/ceiling area, then divide by the coverage printed on each pack (often ~40 ft²).
What R-value do I need?
It depends on your climate zone and where you're insulating — check local code or the DOE recommendations.
Does compressing insulation reduce its R-value?
Yes — batts get their rating at full loft, so squashing a thick batt into a thin cavity lowers its effective R-value. Choose a batt sized for the cavity and fit it snugly without crushing it.