Thermal Conductivity Converter
W/(m·K) · BTU/(h·ft·°F) · cal/(s·cm·K) · kcal/(h·m·°C) · kW/(m·K)
Convert thermal conductivity units instantly — W/(m·K), BTU/(h·ft·°F), cal/(s·cm·K), kcal/(h·m·°C) and more. Essential for mechanical engineers, building physicists, HVAC designers and materials scientists working across SI and imperial specifications.
Reference Table — 1 W/(m·K) equals
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About Thermal Conductivity Units
Thermal conductivity (symbol k or λ) quantifies how readily a material transfers heat by conduction — the higher the value, the faster heat flows through it. It is defined as the heat flux per unit temperature gradient and appears in Fourier's Law of Heat Conduction. Conversions between W/(m·K), BTU/(h·ft·°F), cal/(s·cm·K) and kcal/(h·m·°C) arise constantly when engineering teams work across SI and imperial standards, or when referencing legacy material datasheets from different eras.
🔬 SI Units — W/(m·K) and kW/(m·K)
The watt per metre-kelvin (W/(m·K)) is the SI unit of thermal conductivity, adopted under the International System of Units and now universal in engineering standards such as ISO 10456 for building materials and ASTM C177. It is the most common unit in modern material datasheets, simulation software (ANSYS, Comsol) and academic literature. The kilowatt per metre-kelvin (kW/(m·K) = 1,000 W/(m·K)) is used for highly conductive materials: diamond reaches ~2,000 W/(m·K), and graphene single-layer values above 5,000 W/(m·K) have been measured. Calorie-based units — cal/(s·cm·K) = 418.68 W/(m·K) — belong to the CGS system and appear in older physics and chemistry texts, particularly pre-1970 European and Russian research.
🏗️ Imperial & Legacy Units — BTU/(h·ft·°F) and kcal/(h·m·°C)
BTU per hour per foot per degree Fahrenheit (BTU/(h·ft·°F)) is the primary unit in North American HVAC, construction and building codes such as ASHRAE standards and US federal energy regulations. 1 BTU/(h·ft·°F) = 1.73073 W/(m·K). It directly feeds into R-value calculations, where R = thickness (ft) / k (BTU/(h·ft·°F)). The kilocalorie per hour per metre per degree Celsius (kcal/(h·m·°C)) appears in older European and Soviet-era engineering manuals and some food-processing equipment specifications: 1 kcal/(h·m·°C) = 1.163 W/(m·K). Both units remain common in equipment documentation for legacy industrial installations across the Americas and Eastern Europe.
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Mental Math Tips — Thermal Conductivity
Multiply by 0.578 — or use the rough shortcut "divide by 1.73". So 10 W/(m·K) ≈ 5.78 BTU/(h·ft·°F). For insulation materials below 0.05 W/(m·K), the BTU value is always below 0.03 BTU/(h·ft·°F).
Multiply by ~420 (exact: 418.68). A material at 0.01 cal/(s·cm·K) = 4.19 W/(m·K) — roughly the conductivity of stainless steel. The ×420 factor is easy to remember as "4.2 × 100".
Multiply by 1.163 — nearly 1:1. A material at 2 kcal/(h·m·°C) ≈ 2.33 W/(m·K). For quick mental estimates just treat them as roughly equal, then add ~16% for the precise answer.