Thermal Conductivity Calculator

Thermal conductivity describes how readily a material conducts heat. A high conductivity means heat moves through the material efficiently, while a low conductivity indicates thermal insulation. This calculator rearranges Fourier’s law for steady, one-dimensional conduction through a flat layer: k = Q̇L/(AΔT). In that expression, k is thermal conductivity, Q̇ is the heat transfer rate, L is layer thickness, A is area normal to heat flow, and ΔT is the temperature difference between the two faces. The SI unit is watts per meter-kelvin, written W/(m·K). A temperature difference has the same numerical size in kelvins and degrees Celsius, so a difference measured in °C may be entered directly as kelvins. Absolute temperatures cannot be substituted for ΔT; use the hot-side temperature minus the cold-side temperature. Heat transfer rate is power in watts, not accumulated heat energy in joules. If an experiment records energy over a time interval, divide joules by seconds before using the calculator. Fourier’s law predicts that heat flow increases with conductivity, area, and temperature difference, while a thicker layer reduces it. Solving the law for conductivity is common in guarded hot plate tests, educational laboratories, building-material analysis, and preliminary insulation studies. Representative conductivity values span many orders of magnitude. Gases and foams are low, common building insulation is often around hundredths of a W/(m·K), glass and concrete are higher, and metals can reach tens or hundreds of W/(m·K). This calculation assumes steady conditions, uniform material, constant conductivity, one-dimensional flow, and negligible thermal contact resistance. Convection and radiation at the surfaces must either be controlled or accounted for separately. Moisture, temperature, density, grain orientation, manufacturing variation, and sample defects can all change an apparent conductivity. For layered walls, curved geometries, transient heating, or temperature-dependent properties, use a thermal-resistance network or a more complete heat-transfer model. Experimental values should include uncertainty in thickness, area, temperature sensors, and heat-loss corrections. Use the result as an ideal estimate unless the measurement setup satisfies a recognized test standard.