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Insulation Calculator

Proper insulation saves energy and money. This calculator estimates how much batt or roll insulation you need for walls or attic spaces based on stud spacing and area dimensions.

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Results

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How to Use This Calculator

  1. Measure the area to insulate (length × height for walls, length × width for attics).
  2. Select your stud spacing.
  3. Enter the coverage per roll or bag from the product label.
  4. Review the quantity needed.

How Insulation Calculation Works

This calculator computes the total area, subtracts approximately 6% for framing members (studs, plates, headers), and divides by the coverage per roll or bag. The actual framing percentage varies — walls with many windows or doors have more framing. For attic blown-in insulation, the 'coverage per bag' depends on the desired R-value and depth — check the manufacturer's coverage chart on the bag.

Formula

Total area = Length × Width. Subtract ~6% for studs/framing. Rolls needed = ceil(Insulation area ÷ Roll coverage).

Frequently Asked Questions

What R-value do I need?
Climate-dependent. Zone 1–2 (Southern US): R-13 walls, R-30 attic. Zone 3–4: R-13 to R-15 walls, R-38 attic. Zone 5–7 (Northern US): R-20+ walls, R-49 to R-60 attic. Check the DOE recommendations for your zip code.
Batts vs blown-in insulation?
Batts are easier to DIY and better for walls. Blown-in is better for attics (fills irregular spaces and covers existing insulation). Blown-in typically requires renting a blower machine ($50–$100/day, often free with purchase of 10+ bags).
Should I insulate interior walls?
Not for energy efficiency — they separate conditioned spaces. But insulate interior walls for sound dampening between bedrooms and bathrooms, or between living areas and home offices.

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