Convert thermal conductivity between W/(m·K), BTU/(h·ft·°F), kcal/(h·m·°C) and more — instant, animated, with a full reference table.
Heat • 7 units
All 7 units on the Thermal Conductivity Converter are defined against the Watt/meter·K (W/(m·K)), so each result is one conversion factor away from a single reference rather than the end of a chain of roundings.
The conversion this page is most often opened for is ready before you type anything: 1 W/(m·K) = 0.577789205 BTU/(h·ft·°F). Change either side and every row in the table recalculates with it.
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Thermal conductivity describes how readily a material lets heat pass through it. The concept dates to Joseph Fourier, whose 1822 Théorie analytique de la chaleur set out the law of heat conduction still used today. The modern SI unit, the watt per metre-kelvin, W/(m·K), expresses how many watts flow through a one-metre thickness of material for each kelvin of temperature difference.
Engineers and builders use thermal conductivity constantly: choosing insulation (low values trap heat), sizing heat sinks for electronics (high values such as copper or aluminium move heat away), specifying cookware, and modelling how buildings gain or lose energy. In the US, conductivity is often quoted in BTU/(h·ft·°F) or as the related "k-value" on insulation products, while the rest of the world uses W/(m·K) — making conversion a frequent need.
Quick reference — 1 Watt/meter·K (W/(m·K)) is equal to:
| Watt/centimeter·°C | W/(cm·°C) | 0.01 |
| Kilowatt/meter·K | kW/(m·K) | 0.001 |
| Calorie/(s·cm·°C) | cal/(s·cm·°C) | 0.0023900574 |
| Kilocalorie/(h·m·°C) | kcal/(h·m·°C) | 0.859845228 |
| BTU/(h·ft·°F) | BTU/(h·ft·°F) | 0.577789205 |
| BTU·in/(h·ft²·°F) | BTU·in/(h·ft²·°F) | 6.933471 |
7 units of thermal conductivity, each a fixed multiple of the W/(m·K). The table spans 6,933:1, from BTU·in/(h·ft²·°F) (0.144228 W/(m·K)) to kW/(m·K) (1000 W/(m·K)). Conversion is one multiplication into the base unit and one division out of it, with no lookup table and no approximation.
value_to = value_from × (factor_from ÷ factor_to)1 W/(m·K) = 1 W/(m·K)1 W/(cm·°C) = 100 W/(m·K)1 kW/(m·K) = 1000 W/(m·K)1 cal/(s·cm·°C) = 418.4 W/(m·K)1 kcal/(h·m·°C) = 1.163 W/(m·K)1 BTU/(h·ft·°F) = 1.73073 W/(m·K)1 BTU·in/(h·ft²·°F) = 0.144228 W/(m·K)where:
Assumptions: Factors are exact definitions. Full double precision is carried internally and rounding is applied only for display.
Result25 W/(m·K) = 14.4447 BTU/(h·ft·°F)
Two rows on this page look almost the same and differ by exactly twelve. Conductivity in BTU per hour per foot per degree Fahrenheit and the same quantity expressed per inch of thickness are separated by the twelve inches in a foot, and US insulation products are labelled with the per-inch form. Reading one as the other is a twelve-fold error in the direction that makes insulation look far better or far worse than it is.
Conductivity is also not the quantity most building work actually uses. A k-value belongs to a material, independent of how much of it is present; an R-value belongs to a specific assembly and is thickness divided by conductivity. That is why a material comparison is made in W/(m·K) while a specification is written as an R-value, and why converting between them requires a thickness that the conversion table cannot supply.
Published conductivities are measured under defined laboratory conditions, and real assemblies rarely match them. Fibrous and foam insulation performs worse when compressed, when damp, or when air can move through it; the aged value of some foams differs from the value measured when new. In practice a thermal bridge — a stud, a fixing, a balcony slab — commonly dominates the heat loss of an element whose material conductivity looked excellent on paper.