Insulation Calculator

Free online insulation calculator to estimate the amount of insulation material needed for walls, attics, and ceilings. Calculate based on area, R-value, and insulation type including fiberglass, foam, and cellulose.

The Insulation Calculator helps you estimate the amount of insulation material needed for your home or building project. Enter area dimensions, desired R-value, and insulation type to calculate the quantity of rolls, batts, or bags required.

What is an Insulation Calculator?

An Insulation Calculator is a practical tool for homeowners, contractors, and builders that estimates the quantity of insulation material needed for walls, attics, ceilings, and floors. By entering the area to be insulated, desired R-value (thermal resistance), and insulation type, the calculator determines how many rolls, batts, or bags of insulation you need to purchase, helping you budget accurately and ensure proper thermal performance.

How to Use the Insulation Calculator

Select project type: walls, attic/ceiling, or floor
Enter the area dimensions (length × width or length × height)
Choose the insulation type you plan to use
Select target R-value based on your climate zone and building codes
Enter stud or joist depth to ensure insulation fits
Optionally subtract windows and doors from wall calculations
Click Calculate to see the amount of insulation needed

Insulation Calculation Formulas

1. Area = Length × Width (or Length × Height for walls)

2. Insulation Area = Total Area - (Windows + Doors)

3. Thickness Needed = Target R-Value / R-Value per Inch

4. Quantity = Insulation Area / Coverage per Unit

R-Value Recommendations by Zone

Zone 1-2 (Hot): Attic R-30, Walls R-13, Floor R-13

Zone 3-4 (Warm): Attic R-38, Walls R-13-15, Floor R-19

Zone 5-6 (Cold): Attic R-49, Walls R-19-21, Floor R-25

Zone 7-8 (Very Cold): Attic R-49-60, Walls R-21, Floor R-30

Types of Insulation

Fiberglass Batts/Rolls: R-3 to R-4 per inch, affordable, easy DIY installation

Blown Fiberglass/Cellulose: R-2.2 to R-3.8 per inch, fills gaps, good for attics

Spray Foam: R-3.5 to R-6.5 per inch, air sealing, highest performance

Rigid Foam: R-4 to R-6.5 per inch, moisture resistant, continuous insulation

Mineral Wool: R-3 to R-4 per inch, fire resistant, sound dampening

Tips for Insulation Installation

Always wear protective gear: gloves, long sleeves, dust mask, and eye protection
Don't compress insulation - it reduces R-value significantly
Fill all gaps and voids - even small air leaks reduce effectiveness
Use vapor barriers on the warm side of insulation in cold climates
Ensure proper ventilation in attics to prevent moisture problems
Check local building codes for minimum R-value requirements
Consider hiring professionals for spray foam installation

Understanding R-Value

R-value measures thermal resistance - how well insulation resists heat flow. Higher R-values mean better insulation. R-value depends on thickness, density, and material type. For example, 3.5 inches of fiberglass typically provides R-11 to R-15. Climate zones determine recommended R-values: colder climates need higher R-values. Building codes specify minimum R-values for walls, ceilings, and floors. Adding insulation increases R-value, but compressing it decreases effectiveness. Proper installation without gaps is crucial for achieving rated R-value.

Common Insulation Mistakes

Compressing insulation to fit - reduces R-value by up to 50%
Leaving gaps around outlets, pipes, and wiring
Not using enough insulation for your climate zone
Installing vapor barrier on wrong side
Blocking soffit vents in attic installations
Not accounting for windows and doors in wall calculations

Insulation Calculator

Project Type

Area Dimensions

Insulation Settings

Exclusions (Optional)