Inputs
R
Overall thermal resistance desired for the assembly.
R
Inside + outside surface films, if applicable.
Units:
R per inch
Material library below is in selected unit.
Layers
Add materials; the calculator sums R and reports thickness by layer.
Results
Total R (target)
0.00 R
Total Layer Thickness
0.00 in
| # | Material | R per unit | Required thickness | Layer R |
|---|
Example Material Library
Typical values only; consult manufacturer data.
| Material | R per inch | R per mm |
|---|---|---|
| Fiberglass batt | 3.4 | 0.1339 |
| Cellulose loose‑fill | 3.6 | 0.1417 |
| Mineral wool batt | 4.2 | 0.1654 |
| Expanded polystyrene (EPS) | 4.0 | 0.1575 |
| Extruded polystyrene (XPS) | 5.0 | 0.1969 |
| Polyisocyanurate (Polyiso) | 6.0 | 0.2362 |
| Closed‑cell spray foam | 6.5 | 0.2559 |
| Open‑cell spray foam | 3.8 | 0.1496 |
| Wood fiberboard | 2.9 | 0.1142 |
| Cork board | 3.6 | 0.1417 |
Formula Used
The required thickness for each layer follows the proportional relationship between thermal resistance and thickness.
- Total target resistance:
R_target - Air/surface films (optional):
R_air - Material resistance per unit thickness:
R_unit(R per inch or R per mm)
For a single layer:
Thickness_required = (R_target − R_air) / R_unitFor multiple layers, the calculator distributes required resistance proportionally to each chosen material by its R_unit so the sum reaches R_target after subtracting R_air.
How to Use
- Enter the total R‑value you want for the assembly.
- Optionally include interior/exterior air film resistance.
- Select units, then add one or more material layers.
- Adjust each material’s R per unit to match product data.
- Click Calculate to get thickness by layer and totals.
- Export your table using Download CSV or Download PDF.
- Refine inputs until the design meets performance and buildability.
FAQs
R‑value measures resistance to heat flow. Higher numbers indicate better insulating performance for a given area.
They are typical references. Always verify using the manufacturer’s datasheet for the specific product and density.
Yes. Add multiple layers. The tool sums layer R and total thickness automatically.
This focuses on thermal resistance only. Consult codes about vapor retarders, air barriers, and dew‑point control.
For some materials, yes. Enter the published R per unit for the specific density grade.
Not directly. This calculator assumes continuous layers. For framing effects, use parallel path or area‑weighted methods.
Adjust layer materials or thicknesses. Increase higher‑performing materials to reduce overall thickness where space is limited.