Insulation Calculator – Guide & Formulas
Calculate the total batts, rolls, or blown insulation volume required to insulate attic, walls, or crawlspaces to target R-values.
Estimate the amount of fiberglass, cellulose, or rockwool insulation needed for your energy efficiency project. Calculate the number of rolls, batts, or loose-fill bags needed to achieve a target R-Value.
Key Takeaway
Use the free Insulation Calculator to calculate the total batts, rolls, or blown insulation volume required to insulate attic, walls, or crawlspaces to target r-values. Get instant results with step-by-step explanations.
How to Use the Insulation Calculator
- Enter the length and width of the walls, attic floor, or joist cavity space.
- Select your framing spacing (typically 16" or 24" on center) and cavity depth.
- Check standard recommendations based on local climate zones to find the target R-Value.
The Formula
Variable Definitions
- A: Net insulation coverage area in square feet
- N_batts: Number of pre-cut insulation batts needed
Insulating an Attic Space
A standard home attic measures 40 ft long by 30 ft wide. Estimate the rolls of R-30 insulation needed (each roll covers 48.9 sq ft).
- Step 1: Calculate total attic area: 40 × 30 = 1,200 sq ft.
- Step 2: Determine rolls: 1,200 / 48.9 = 24.54 rolls.
- Step 3: Add 5% waste margin: 24.54 × 1.05 = 25.77 rolls.
- Step 4: Order 26 total rolls of R-30 insulation.
Frequently Asked Questions
What is R-Value?
R-Value is a measure of thermal resistance. The higher the R-value, the greater the insulating effectiveness of the material.
What are the insulation standards for attics?
The US Department of Energy recommends R-38 to R-60 for attic spaces in cold climates, and R-30 to R-49 in warmer regions.
What is the difference between batts and rolls?
Batts are pre-cut to standard lengths (usually 48" or 93" to fit standard wall cavities). Rolls are continuous lengths that you cut manually, ideal for long runs in floors or attics.