Insulation Calculator

Estimate insulation area, required R-value layers, packages, batts, rolls or bags, waste allowance, and material cost for walls and attics.

Project Area

Project Type

Number of Equal Areas

Room Length (ft)

Room Width (ft)

Wall Height (ft)

Doors and Windows (sq ft)

Enter the combined area of doors, windows, and other wall sections that will not receive insulation.

Insulation Product

Product Type

Coverage Per Package (sq ft)

Product R-Value Per Layer

Target R-Value

Waste Allowance (%)

Price Per Package ($)

Use the coverage and R-value printed on the selected product. Loose-fill bag coverage changes with the target R-value, so use the bag chart for the R-value being installed.

Insulation Estimate

Gross Surface Area —

Excluded Openings —

Net Insulation Area —

Calculated R-Value Layers —

Coverage Before Waste —

Waste Allowance —

Total Coverage Required —

Packages Required —

Coverage Purchased —

Estimated Extra Coverage —

Estimated Material Cost —

R-value stacking is a planning calculation only. Available cavity depth, compression, ventilation, vapor control, fire protection, product compatibility, and local building requirements determine whether multiple layers are suitable.

How the Insulation Calculator Works

The calculator finds the net surface area, determines the number of product layers needed to meet the target R-value, adds waste, and divides the required coverage by the coverage provided by one package.

Packages = Total Coverage Required ÷ Coverage Per Package

What Is R-Value?

R-value measures resistance to heat flow. A higher R-value provides greater resistance, but the correct target depends on climate, building location, assembly type, energy code, and the existing insulation.

Do Insulation R-Values Add Together?

R-values generally add when compatible insulation layers are installed correctly without harmful compression or gaps. Two R-15 layers theoretically provide R-30. However, the building assembly must have enough space and must meet moisture, ventilation, fire, and manufacturer requirements.

Why Insulation Should Not Be Compressed

Fiberglass insulation depends on trapped air to provide its rated performance. Compressing a thick batt into a shallow cavity can reduce its effective R-value. Select insulation designed for the available cavity depth.

Loose-Fill Insulation Coverage

Loose-fill insulation bags cover different areas depending on the desired R-value and installed depth. Use the coverage chart printed on the bag rather than a general square-foot assumption.

Before Installing Insulation

Air sealing, moisture control, ventilation, electrical clearances, recessed fixtures, combustion appliances, and fire blocking may need attention before insulation is added. Confirm local requirements and product instructions.