Calculator Inputs
Plotly Graph
This chart shows conductivity changes across the selected thickness range, while resistance and area stay fixed.
Example Data Table
| Material | Thermal Resistance | Resistance Unit | Thickness | Thickness Unit | Area | Area Unit |
|---|---|---|---|---|---|---|
| Fiberglass board | 2.5 | SI | 50 | mm | 1 | m2 |
| Mineral wool slab | 3.2 | SI | 75 | mm | 1.2 | m2 |
| Foam insulation panel | 4.8 | SI | 100 | mm | 2 | m2 |
| Dense concrete wall | 0.12 | SI | 150 | mm | 1.5 | m2 |
| Wood section | 1.1 | SI | 25 | mm | 0.8 | m2 |
Formula Used
The calculator uses the flat layer conduction relationship between thermal resistance and thermal conductivity.
R = L / (k × A)
Where:
- R = thermal resistance in m²·K/W
- L = thickness in meters
- k = thermal conductivity in W/m·K
- A = area in square meters
Rearranging for conductivity gives:
k = L / (R × A)
This page also estimates U-value = k / L and heat flow per degree temperature difference using Q/K = kA/L.
How to Use This Calculator
- Enter the thermal resistance for the tested layer.
- Select SI or imperial resistance units.
- Enter the layer thickness and choose its unit.
- Enter the effective heat transfer area.
- Set a chart thickness range for comparison.
- Press Calculate Now to view results.
- Review conductivity, U-value, and heat flow output.
- Download the result set as CSV or PDF.
FAQs
1. What does thermal conductivity represent?
Thermal conductivity shows how easily heat moves through a material. Lower values usually mean better insulation, while higher values indicate faster heat transfer through the layer.
2. Why does the calculator need area?
Area affects total resistance in the conduction equation used here. A larger heat transfer surface changes the conductivity result when resistance is based on the whole tested layer.
3. Can I use imperial R-values?
Yes. The tool converts imperial resistance values into SI form before calculation. That keeps the conductivity result consistent in W/m·K.
4. What is the difference between conductivity and U-value?
Conductivity is a material property. U-value describes heat transfer through a specific thickness or assembly. U-value depends on geometry, while conductivity belongs to the material itself.
5. Does this work for multilayer walls?
It works best for a single equivalent layer. For multilayer systems, use total thermal resistance first, then convert carefully if you want an effective conductivity value.
6. Why does the graph change with thickness?
The graph holds resistance and area constant, then recalculates conductivity for each thickness. It helps visualize how inferred conductivity changes across alternative layer dimensions.
7. What units does the result use?
The main conductivity result uses watts per meter-kelvin, written as W/m·K. That is the standard engineering unit for thermal conductivity.
8. Is this calculator suitable for insulation selection?
Yes, for screening and comparison. Final design choices should still consider moisture behavior, compression, temperature range, fire requirements, and manufacturer test standards.