Thermal Conductivity Converter
Convert W/(m·K), BTU·in/(hr·ft²·°F), kcal/(hr·m·°C), and other thermal conductivity units.
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Base Unit
Relative Value
*Diagram shows values relative to the selected base unit (W/(m·K)).
Unit Information
What is Watt per meter-Kelvin (W/(m·K))?
Watt per meter-Kelvin (W/(m·K) or W·m⁻¹·K⁻¹) is the SI unit of thermal conductivity. It represents the amount of heat (in Watts) that flows through a 1-meter thick material with a 1-square-meter area when there is a temperature difference of 1 Kelvin (or 1 degree Celsius) across that thickness. It is the standard unit in scientific and most international engineering contexts.
What is Watt per centimeter-Kelvin (W/(cm·K))?
This unit is simply a variation of the SI unit using centimeters instead of meters. Since 1 meter = 100 centimeters, 1 W/(cm·K) is equivalent to 100 W/(m·K). It might be used for materials where properties are measured over smaller scales.
What is Kilowatt per meter-Kelvin (kW/(m·K))?
A kilowatt per meter-Kelvin is 1000 W/(m·K). This larger unit would be used for materials with exceptionally high thermal conductivity, such as certain advanced composites or superfluids.
What is Calorie per second-centimeter-°C?
This is a CGS (centimeter-gram-second) based unit of thermal conductivity. It uses the calorie as the unit of heat energy. Its conversion to W/(m·K) depends on the specific definition of the calorie (e.g., International Table calorie).
What is Kilocalorie per hour-meter-°C?
This is a metric unit often seen in older European engineering contexts. It measures heat transfer in kilocalories over a longer period (hour), making the numerical values smaller and sometimes more convenient for building materials.
What is BTU per hour-foot-°F?
This imperial unit measures thermal conductivity in terms of British Thermal Units (BTU) per hour, for a material of one foot thickness with a temperature difference of one degree Fahrenheit. It's a direct counterpart to the W/(m·K) unit in the imperial system.
What is BTU inch per hour-square foot-°F?
This is a common imperial unit for thermal conductivity, particularly in the North American building industry. It's often called the 'k-value' and is the basis for calculating R-values for insulation. It conveniently uses inches for the thickness, which is how insulation is typically measured.
Formulas
q = -k * A * (ΔT / Δx)
Fourier's Law of Heat Conduction, where 'q' is heat flow rate, 'k' is thermal conductivity, 'A' is area, 'ΔT' is temperature difference, and 'Δx' is thickness.
R-value (US) = thickness (in) / k-value
The thermal resistance (R-value) of insulation in the US is its thickness in inches divided by its thermal conductivity in BTU·in/(hr·ft²·°F).
R-value (SI) = thickness (m) / k-value
The R-value in the SI system is its thickness in meters divided by its thermal conductivity in W/(m·K).
U-value = 1 / R-value
The U-value (Overall Heat Transfer Coefficient) is the reciprocal of the R-value. A lower U-value indicates better insulation.
1 W/(m·K) ≈ 6.933 BTU·in/(hr·ft²·°F)
A useful conversion factor between the common SI and US imperial units for insulation.
Key Reference Points
- Silver: ~429 W/(m·K)
- Copper: ~401 W/(m·K)
- Aluminum: ~237 W/(m·K)
- Steel (Carbon): ~40-60 W/(m·K)
- Concrete: ~0.8 - 1.7 W/(m·K)
- Glass: ~1 W/(m·K)
- Water: ~0.6 W/(m·K)
- Wood (Pine): ~0.12 W/(m·K)
- Fiberglass Insulation: ~0.04 W/(m·K)
- Air (still): ~0.026 W/(m·K)
Did You Know?
Metals like copper (k ≈ 400 W/(m·K)) and silver (k ≈ 429 W/(m·K)) are excellent thermal conductors due to the free movement of electrons, making them ideal for heat sinks and cookware.
Materials like air (k ≈ 0.026 W/(m·K)), styrofoam (k ≈ 0.033 W/(m·K)), and fiberglass (k ≈ 0.04 W/(m·K)) have low thermal conductivity, making them effective insulators by impeding heat flow.
Aerogels are synthetic porous ultralight materials derived from a gel, in which the liquid component of the gel has been replaced with a gas. They can have extremely low thermal conductivities, some as low as 0.013 W/(m·K), making them among the best known thermal insulators.
Surprisingly, diamond has one of the highest thermal conductivities of any bulk material, around 2000-2200 W/(m·K), which is about five times higher than copper. This is due to its strong covalent bonding and lattice structure allowing efficient phonon (heat vibration) transport.
The thermal conductivity of most materials varies with temperature. For metals, it generally decreases with increasing temperature, while for non-metals and insulators, it often increases.
Heat sinks in electronic devices are designed to have a high thermal conductivity (usually made of aluminum or copper) and a large surface area to efficiently dissipate heat generated by components like CPUs.
When a liquid droplet is placed on a surface significantly hotter than its boiling point, a layer of vapor instantly forms underneath it. This vapor layer has low thermal conductivity and insulates the droplet, causing it to skitter across the surface for a surprisingly long time.
TIM, or thermal paste, is used between a heat source (like a CPU) and a heat sink. It fills in microscopic air gaps between the two surfaces. Since air is a poor conductor, the TIM, which has a higher thermal conductivity, greatly improves the heat transfer.
A vacuum flask (or thermos) uses a near-vacuum between two walls to minimize heat transfer by conduction and convection. The surfaces are also often silvered to reduce heat transfer by radiation.
In crystalline solids, heat is conducted by 'phonons,' which are quantized modes of vibration. The way phonons travel and scatter within the material's lattice determines its thermal conductivity.
Graphene, a single layer of carbon atoms, has an exceptionally high thermal conductivity, even greater than diamond. This property makes it a promising material for future thermal management applications in electronics.
Some materials, like wood or layered composite materials, are anisotropic, meaning their thermal conductivity is different in different directions. Heat travels more easily along the grain of wood than across it.
Fat has a lower thermal conductivity than muscle, which is why it acts as a natural insulator for the body, helping to conserve heat in cold environments.
Water has a much higher thermal conductivity than most liquids, but it's still far lower than metals. This property is vital for its role in regulating climate and in biological systems.
This law states that for metals, the ratio of the thermal conductivity to the electrical conductivity is directly proportional to the temperature. This reflects the fact that in metals, both heat and electricity are primarily carried by free electrons.
Thermal effusivity is a measure of a material's ability to exchange thermal energy with its surroundings. It's related to thermal conductivity, density, and specific heat. It explains why a metal floor feels colder than a wooden floor at the same temperature, even though the wood has lower conductivity.
A thermal diode is a device that allows heat to flow preferentially in one direction. These are being developed for advanced thermal management systems and energy harvesting.
The design of cookware often involves combining materials with different thermal conductivities. A pot might have a copper bottom (high conductivity) for even heating, but a stainless steel or plastic handle (low conductivity) to stay cool.