How to use this calculator
- Enter Target R-value — or tap a preset badge to auto-fill a typical value.
- Enter Material.
- Press Calculate. The highlighted row is your order quantity; the note beneath it translates the number into real-world terms.
Formula & constants
Depth = target R ÷ R-per-inch: fiberglass batt 3.2, blown fiberglass 2.5, blown cellulose 3.5, open-cell foam 3.7, closed-cell foam 6.5. Attics in most US zones target R-49 to R-60. 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
Efficiency upgrades interact: better insulation and correct R-values shrink the heating and cooling load, which shrinks the solar array needed to offset it. Size loads first, generation second.
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 r-value calculator:
- Insulation Calculator — R-value is the measure of insulation effectiveness.
- BTU Calculator — Higher R-value reduces BTU requirements.
- HVAC Size Calculator — Recommended R-values affect HVAC sizing.
- Window Cost Calculator — Windows have their own U-factor, not R-value.
Frequently asked questions
What R-value should an attic have?
R-49 minimum in most of the US, R-60 in cold zones per IECC — that’s 14–17 in of blown cellulose.
Does doubling insulation double savings?
No — returns diminish. Going R-19→R-49 matters far more than R-49→R-60; air sealing often beats both.
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.