🧱 Thermal Resistance Calculator
Work out the thermal resistance of a flat material layer and how much heat flows through it for a given temperature difference and area.
What This Calculator Does
Thermal resistance (R-value) describes how well a material layer resists the flow of heat — higher R means better insulation. This calculator finds the R-value of a single flat layer and estimates the resulting steady-state heat flow through it.
The Formula
For a flat layer, thermal resistance is R = L / k, where L is the layer thickness and k is the material’s thermal conductivity. The rate of heat flow through the layer is then Q = (A · ΔT) / R, where A is the surface area and ΔT is the temperature difference across the layer. The U-value, commonly used in building insulation, is simply 1/R.
Note: This calculation is for a single uniform layer under steady-state conditions, for general educational and planning purposes. Real walls and assemblies usually have multiple layers in series (their resistances simply add), plus air films and thermal bridging that this simplified model does not account for.