Inputs
white themeResults
Adjusted area
—
ft² (after unit conversion and waste)
R-value to add
—
R (max of target minus existing, not below 0)
Estimated thickness
—
inches (using selected type R per inch)
Packages required (coverage-based)
—
rounded up for ordering
Batt piece area
—
ft² (cavity width × piece length)
Pieces needed
—
rounded up (raw: —)
Packages by pieces
—
rounded up using pieces per package
Raw package count (not rounded): —
Scenario table
| # | Assembly | Type | Area (ft²) | Waste % | Target R | Existing R | R add | Thickness (in) | Mode | Coverage/Package (ft²) | Packages (raw) | Packages (rounded) | Pieces (rounded) | Pkgs by pieces |
|---|
Formulas used
Core calculations
- Area_ft² = Area_input × ( 10.7639 if input is m² else 1 )
- Area_adj = Area_ft² × (1 + Waste%/100)
- R_add = max(0, R_target - R_existing)
- Thickness_in = R_add / R_per_inch (informational)
Package math
- Simple mode: Packages_raw = Area_adj / Coverage_per_package_ft²
- Advanced density: thickness t_in = R_add / R_per_inch, bag volume V_bag = Bag_weight / Settled_density (ft³)
- Coverage per bag A_bag = V_bag / (t_in/12) (ft²)
- Then Packages_raw = Area_adj / A_bag
- Packages_rounded = ceil(Packages_raw)
Batt cavity helper
- Typical cavity width ≈ Spacing_in − 1.5 inches (adjust if product width differs).
- Piece area (ft²) = (Cavity_width_in/12) × (Batt_length_in/12).
- Pieces needed (raw) = Area_adj / Piece_area_ft², rounded up for ordering.
- Packages by pieces = ceil( Pieces_rounded / Pieces_per_package ).
Always confirm with manufacturer coverage charts and local codes. This tool estimates for planning.
How to use this calculator
- Select the surface Assembly and Insulation type. The R per inch field auto-fills but can be edited.
- Enter total Area directly or use Length × Width. Choose units.
- Set Target R and any Existing R. Or choose a Climate zone preset and click Apply to target R.
- Pick a calculation mode:
- Simple: enter the label Coverage per package at your target R or load a preset.
- Advanced density: provide bag weight and settled density; the tool computes coverage per bag using thickness.
- Batt users: expand the Batt cavity helper to estimate pieces and packages based on stud spacing, cavity width, and piece length.
- Adjust waste allowance. Click Calculate. Review results and optionally Add to table. Export Results or the Scenario table as CSV or PDF.
FAQs
Use a conservative estimate for existing R or divide the area into zones and run separate calculations. Consider air sealing before adding loose-fill.
Presets are example placeholders. Always replace them with the exact coverage table printed on your product packaging for the specific R target.
Typical values: cellulose ~3.7, blown fiberglass ~2.8–3.2, fiberglass batt ~3.2–3.7, rockwool batt ~4.0, open-cell spray foam ~3.6, closed-cell spray foam ~6.0–7.0. Verify with manufacturer data.
Yes. Energy codes specify recommended R-values by climate zone and assembly. Use the climate zone preset as a starting point and confirm with local requirements.
For batts, choose spacing and cavity width that match your structure and product width. The helper estimates piece counts and packages. Add extra waste for complex framing.