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Insulation Calculator

Calculate insulation thickness, materials, and R-value needs.

Last updated: June 13, 2026

Calculator

Area to Insulate

sq ft

Insulation Type

Target R-Value

Results

Thickness Required9.4"

For R-30 with batts

Batts Needed25 rolls

~40 sq ft per roll

Estimated Cost$650

Materials only

R-Value per Inch3.2

How to Use This Calculator

1Enter the area to insulate in square feet.
2Select your climate zone or desired R-value.
3View batts or rolls needed, thickness, and cost estimate.

Formula Explanation

Insulation coverage is calculated from area with waste factor. R-value recommendation is based on climate zone and application (attic, wall, floor).

Rolls Needed = Area ÷ Roll Coverage × Waste Factor Batts Needed = Area ÷ Batt Coverage × Waste Factor

Variables:

AreaTotal area to insulate in square feet

Roll CoverageSquare feet per roll (varies by product)

Waste FactorTypically 1.1 (10% waste) for standard areas

Worked Examples

1,200 sq ft attic, R-38

1. R-38 fiberglass = ~12 inches thick
2. Rolls at 40 sq ft coverage: 1,200 ÷ 40 = 30
3. With 10% waste: 33 rolls

Result: 33 rolls of R-38 insulation (~12" thick)

Why Use This Calculator

Recommends R-value based on your climate zone.
Calculates both batt and roll quantities.
Includes waste factor for cuts around obstacles.
Helps compare insulation types and costs.

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Tips & Best Practices

Attics benefit most from insulation upgrades — heat rises.
Don't compress insulation — it reduces R-value.
Seal air leaks before insulating for maximum effectiveness.
Wear protective equipment: long sleeves, gloves, mask, and goggles.

Common Mistakes to Avoid

❌ Compressing insulation to fit in a smaller space.

✅ Compressed insulation loses R-value. Use the correct thickness for your target R-value.

❌ Insulating without air sealing first.

✅ Air leaks can account for 30% of heating/cooling loss. Seal gaps around pipes, wires, and fixtures before insulating.

Frequently Asked Questions

What R-value do I need?

It depends on your climate zone and location in the home. Attics: R-38 to R-60. Walls: R-13 to R-21. Floors: R-19 to R-30. Check the DOE recommendations for your zip code.

What type of insulation is best?

Fiberglass batts are most cost-effective for open stud bays. Blown-in cellulose or fiberglass is best for attics. Spray foam provides the best air sealing but costs more.

How much does insulation save on energy bills?

Properly insulating an uninsulated home can reduce heating/cooling costs by 20-30%. Adding insulation to an already-insulated attic from R-19 to R-49 typically saves 10-15%.

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Disclaimer: This calculator is provided for informational and educational purposes only. Results are estimates and should not be used as a substitute for professional advice. RediCalc.com makes no guarantees regarding the accuracy, completeness, or suitability of any calculations. Always consult a qualified professional before making financial, health, construction, or other important decisions.

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