Thermal Conductivity and R-Value Calculator
Works out a material’s conductivity from a heat flow measurement.
Thermal conductivity (k)
— W/m·K
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
R-value — m²·K/W
R-value, US units — h·ft²·°F/BTU
U-value — W/m²·K
Reading this —
The formula
k = Q d ÷ (A ΔT) R = d ÷ k U = 1 ÷ R
Steady heat flow straight through a flat layer, with temperatures measured at its faces. A U-value quoted for a whole wall also includes air films, so it reads lower than this figure.
What to watch out for
To go the other way, and get a heat flow from a known k, use the heat transfer calculator.
Frequently Asked Questions
What is k if 20 W crosses 1 m² of 10 cm material with a 20 °C difference?
0.1 W/m·K, which is about what a timber wall gives.
What are typical values?
Roughly 400 W/m·K for copper, 50 for steel, 1 for glass, 0.15 for timber, 0.04 for insulation and 0.025 for still air.