Insulation Calculator
Estimate the square footage, volume, and number of standard batts or rolls of insulation needed to insulate walls, ceilings, or attics.
Calculation Results
The net flat surface area to insulate.
The total volume of insulation material needed.
Estimated count of standard 15-inch wide by 48-inch long batts required for standard 16" on-center framing.
How This Calculator Works
To calculate insulation materials for your project:
- Enter the length and width of the ceiling, wall, or floor cavity to be insulated.
- Specify the desired thickness of the insulation layer in inches (a standard 2x6 wall cavity takes a 5.5 to 6-inch thick batt, R-19).
- The calculator determines total surface area, cubic volume, and standard batt counts.
Formula & Calculations
Insulation coverage and volume calculations are based on standard geometry and material sizes:
Coverage Area = Length × Width
Insulation Volume = Coverage Area × (Thickness in inches / 12)
Standard batts count is estimated by dividing total area by the surface area of a standard batt (e.g. 15 inches × 48 inches = 5.0 sq ft):
Batts Required = ceil(Coverage Area / 5.0)
Step-by-Step Calculation Examples
Typical Wall Cavity Insulation (40ft x 12ft)
Estimating insulation requirements for a standard 480 sq ft exterior wall with 6 inches thickness.
- length: 40
- width: 12
- thickness: 6
- area: 480.00 sq ft
- volume: 240.00 cu ft
- batts_needed: 96
Frequently Asked Questions
What is R-value in insulation?
R-value measures thermal resistance—the material's ability to resist heat flow. A higher R-value means better insulating performance. R-value is determined by insulation type, density, and thickness.
How thick should insulation be in an attic?
In most climates, standard building guidelines suggest an attic R-value between R-38 and R-60, which requires approximately 12 to 18 inches of loose-fill fiberglass or cellulose insulation.
What size are standard insulation batts?
Batts are cut to fit standard framing spaces: either 15 inches wide (for 16-inch on-center studs) or 23 inches wide (for 24-inch studs). They are typically sold in 48-inch (4-foot) or 93-inch (7.75-foot) lengths.
What is the difference between faced and unfaced insulation?
Faced insulation has a paper or foil backing (kraft paper) that acts as a vapor barrier to prevent moisture from passing through. Unfaced insulation has no backing and is used in interior walls or to layer over existing attic insulation.
Can I overlay faced insulation on top of old insulation?
No. Laying faced insulation over existing insulation traps moisture between the layers, which leads to mold growth. Always use unfaced insulation when layering on top of existing attic insulation.