Thermal Conductivity Converter
Convert thermal conductivity (k-value) between W/(m·K), W/(cm·°C), kW/(m·K), calorie and kilocalorie units and the imperial Btu-inch and Btu-foot units. Enter a value, choose the units and read the result instantly.
Select two units to see the conversion factor.
Thermal conductivity (W/(m·K)) is a material property. It is not thermal resistance (K/W), thermal resistivity (m·K/W) or a heat transfer coefficient (W/(m²·K)).
Thermal Conductivity Formula
Thermal conductivity k is heat flow × thickness ÷ (area × temperature difference): k = Q·L ÷ (A·ΔT), in W/(m·K). All units are a fixed multiple of W/(m·K). Result = value × (source factor ÷ target factor). Exact building blocks: 1 Btu (IT) = 1,055.05585262 J, 1 ft = 0.3048 m, 1 in = 0.0254 m, 1 °F interval = 5/9 K, 1 cal (IT) = 4.1868 J, 1 cal (th) = 4.184 J. For example 1 Btu(IT)·in/(h·ft²·°F) ≈ 0.14413 W/(m·K).
What Is Thermal Conductivity?
Thermal conductivity says how easily heat passes through a material. A high value, like copper at about 400 W/(m·K), moves heat quickly; a low value, like mineral wool near 0.04 W/(m·K), is a good insulator. By definition it is the heat flow through a 1 m thick, 1 m² slab when its two faces differ by 1 K: k = Q·L ÷ (A·ΔT).
The unit contains a length because conductivity is independent of the size of the sample. That separates it from thermal resistance (K/W, depends on an object’s size), thermal resistivity (the reciprocal of conductivity, m·K/W) and the heat transfer coefficient (W/(m²·K), for a surface or layer). Conductivity of a layer divided by its thickness gives a coefficient; the converter does not do that.
Imperial units are common in insulation data: the Btu·in/(h·ft²·°F) is the k-value per inch of thickness, while the Btu·ft version is per foot. IT and thermochemical calories and Btu differ by about 0.07 %, so both are listed. The temperature degree is an interval, so no offsets are used.
Supported Units
This converter supports the following 13 thermal conductivity units. The last column gives the value of each unit in the base unit W/(m·K).
| Unit | Symbol | Value in W/(m·K) |
|---|---|---|
| Watt per meter per kelvin | W/(m·K) | 1 |
| Watt per centimeter per °C | W/(cm·°C) | 100 |
| Kilowatt per meter per kelvin | kW/(m·K) | 1,000 |
| Calorie (IT) per second per cm per °C | cal(IT)/(s·cm·°C) | 418.68 |
| Calorie (th) per second per cm per °C | cal(th)/(s·cm·°C) | 418.4 |
| Kilocalorie (IT) per hour per meter per °C | kcal(IT)/(h·m·°C) | 1.163 |
| Kilocalorie (th) per hour per meter per °C | kcal(th)/(h·m·°C) | 1.162222222 |
| Btu (IT) inch per second per sq. foot per °F | Btu(IT)·in/(s·ft²·°F) | 519.2203999 |
| Btu (th) inch per second per sq. foot per °F | Btu(th)·in/(s·ft²·°F) | 518.8731617 |
| Btu (IT) foot per hour per sq. foot per °F | Btu(IT)·ft/(h·ft²·°F) | 1.730734666 |
| Btu (th) foot per hour per sq. foot per °F | Btu(th)·ft/(h·ft²·°F) | 1.729577206 |
| Btu (IT) inch per hour per sq. foot per °F | Btu(IT)·in/(h·ft²·°F) | 0.1442278889 |
| Btu (th) inch per hour per sq. foot per °F | Btu(th)·in/(h·ft²·°F) | 0.1441314338 |
How to Use the Thermal Conductivity Converter
- Type the thermal conductivity in the value box. Decimals and scientific notation such as 0.0025 or 2.5e-3 are accepted.
- Choose the From unit and the To unit.
- The result appears instantly, or press Convert Now. Very large or very small results are shown in scientific notation.
- Use Swap Units to reverse the conversion, Copy Result to copy the answer, open Show this value in all units for a full list, and Clear to start again.
Step-by-step by hand
- Find the size of each unit in the common base unit (W/(m·K)): 1 Btu(IT)·in/(h·ft²·°F) = 0.1442278889 W/(m·K) and 1 W/(m·K) = 1 W/(m·K).
- Divide the source size by the target size to get the conversion factor: 0.1442278889 ÷ 1 = 0.1442278889, so 1 Btu(IT)·in/(h·ft²·°F) = 0.1442278889 W/(m·K).
- Multiply by your value: 0.25 Btu(IT)·in/(h·ft²·°F) × 0.1442278889 = 0.03605697222 W/(m·K).
Thermal conductivity cannot be negative, so only zero and positive values are accepted.
Common Thermal Conductivity Conversions
- Insulation (imperial to metric): 0.25 Btu·in/(h·ft²·°F) equals 0.03605697222 W/(m·K).
- Metric to imperial: 0.04 W/(m·K) equals 0.2773388719 Btu·in/(h·ft²·°F).
- Copper: 400 W/(m·K) equals 231.1157266 Btu·ft/(h·ft²·°F).
- Per centimetre: 2 W/(cm·°C) equals 200 W/(m·K).
- Calorie units: 0.001 cal/(s·cm·°C) equals 0.41868 W/(m·K).
- Kilocalorie per hour: 0.5 kcal/(h·m·°C) equals 0.5815 W/(m·K).
W/(m·K) to Btu·in/(h·ft²·°F)
Quick reference for frequently used values
| W/(m·K) | Btu·in/(h·ft²·°F) | Btu·ft/(h·ft²·°F) | kcal/(h·m·°C) |
|---|---|---|---|
| 0.03 | 0.208004154 | 0.0173336795 | 0.02579535684 |
| 0.04 | 0.2773388719 | 0.02311157266 | 0.03439380911 |
| 0.1 | 0.6933471799 | 0.05777893165 | 0.08598452279 |
| 0.5 | 3.466735899 | 0.2888946583 | 0.4299226139 |
| 1 | 6.933471799 | 0.5777893165 | 0.8598452279 |
| 15 | 104.002077 | 8.666839748 | 12.89767842 |
| 400 | 2,773.388719 | 231.1157266 | 343.9380911 |
Where and Why This Conversion Is Used
- Building insulation: compare k-values from US and metric data sheets.
- Mechanical design: heat paths through metals, plastics and ceramics.
- Electronics: thermal interface materials and heat spreaders.
- Materials science and teaching: older calorie-based tables.
Limitations
- Conductivity varies with temperature, moisture and density; the converter changes units only.
- It does not convert to R-value, thermal resistance or heat transfer coefficient.
- The Btu·in and Btu·ft versions differ by a factor of 12, so check which one a source uses.
Important Differences Between Related Heat Quantities
- Specific heat capacity, J/(kg·K): energy needed to warm one kilogram of a material by one kelvin. It is not the total heat capacity of an object (J/K), which also depends on how much material there is, and it is not molar heat capacity (J/(mol·K)).
- Heat density, J/m²: heat or radiant energy delivered per unit area over a period. Heat flux density, W/m² is the rate of that transfer, energy per area per time. They are not interchangeable.
- Heat flux density, W/m² is heat flow per area. The heat transfer coefficient, W/(m²·K) is heat flux per kelvin of temperature difference, so heat flux = coefficient × temperature difference.
- Thermal conductivity, W/(m·K) is a material property. The heat transfer coefficient is a property of a surface or an assembly, and thermal resistance, K/W belongs to one specific object. Resistance is not conductivity or resistivity: R = L ÷ (k × A) for a slab.
- Temperature interval vs temperature: a difference of 10 °C is a difference of 18 °F. A reading of 10 °C is 50 °F. Every unit here that contains “per degree” or “K” uses intervals, so no offset is ever applied.
Each converter changes units within one quantity only. Related tools: Temperature Interval, Thermal Expansion, Thermal Resistance, Thermal Conductivity, Specific Heat Capacity, Heat Density, Heat Flux Density, Heat Transfer Coefficient, Fuel Efficiency - Mass and Fuel Efficiency - Volume.