Free Insulation Calculator — Plan Added R-Value Without Guessing Package Count

This free insulation calculator helps you figure out how much more insulation a space needs to reach a target R-value. It works for attics, exterior walls, crawl spaces, and basements, then converts the added thermal value into approximate thickness, package count, total coverage, and material cost. That makes it a useful planning tool for retrofit weatherization, unfinished spaces, and energy-upgrade bids.

Because each insulation product performs differently per inch, the calculator also changes the thickness requirement when you switch from fiberglass batts to blown-in, spray foam, or rigid board. That is helpful when depth is limited and the crew needs to know whether the chosen assembly can realistically hit the target in the available cavity.

When existing insulation should be measured before ordering more

A frequent mistake is ordering new material from the target R-value only and forgetting the insulation that is already in place. In attics and older exterior walls, the existing assembly may be thin, compressed, uneven, or partly missing. If you do not account for that correctly, it is easy to overspend on material or still miss the intended thermal target.

Use this calculator as a practical estimator, then confirm actual cavity depth, code minimums, vapor control, and installation method before starting work. Air sealing, moisture conditions, and local energy-code requirements can matter just as much as the insulation thickness itself.