How to use this calculator
- Enter Area to insulate in sq ft.
- Enter Coverage per unit in sq ft.
- Press Calculate. The highlighted row is your order quantity; the note beneath it translates the number into real-world terms.
Formula & constants
Divide area by the coverage printed per bag or batt package: fiberglass batts ~40–90 sq ft/pack by R-value, blown fiberglass ~40–75 sq ft/bag at attic depths. Add 5% for framing irregularity. Every default in the fields above is editable — when your supplier’s spec sheet lists a different density, coverage rate or price, enter that number instead. The waste and compaction allowances follow common trade practice; see our methodology page for the derivation of each formula and the standards it references.
Where this fits in the project
Interior finishing runs framing-out: studs, insulation, drywall, then paint and floor coverings. Measure once and reuse the same wall and floor areas across each material takeoff.
How this connects to your project
No quantity stands alone — each material in the chain depends on the ones around it. These are the planning steps that pair with the insulation calculator:
- Drywall Calculator — Insulation is installed before drywall.
- R-Value Calculator — R-value is the measure of insulation effectiveness.
- Stud Calculator — Batt insulation fits between wall studs.
- HVAC Size Calculator — Better insulation reduces HVAC size requirements.
- BTU Calculator — Insulation quality affects heating and cooling BTU needs.
- Siding Calculator — Wall insulation sits behind exterior siding.
Frequently asked questions
Batts or blown-in for attics?
Blown-in wins in open attics — seamless coverage over joists; batts suit walls and accessible cavities.
Can new insulation go over old?
Yes if the old layer is dry and unfaced — add unfaced material on top; never trap a vapor barrier between layers.
Last verified: — prices reflect current national averages. See our methodology.
Estimates are for planning. Material densities, coverage rates and prices vary by region and supplier — confirm final quantities before ordering, and check local code where structural or electrical work is involved.