Understanding Watts per Metre-Kelvin to BTU per Hour-Foot-Degree Fahrenheit Conversion
The watt per metre-kelvin (W/(m·K)) is the SI measure of thermal conductivity, the rate heat passes through a material of given thickness per degree of temperature difference. The BTU per hour-foot-degree Fahrenheit is the traditional US engineering unit, expressing the same property with thickness in feet. This pairing is common in HVAC, process-plant and pipe-insulation calculations where American handbooks quote k in BTU/(h·ft·°F).
Conversion Formula
To convert Watts per Metre-Kelvin to BTU per Hour-Foot-Degree Fahrenheit, multiply by this factor:
Step-by-Step Example
Convert 25 Watts per Metre-Kelvin to BTU per Hour-Foot-Degree Fahrenheit.
How to Convert Watts per Metre-Kelvin to BTU per Hour-Foot-Degree Fahrenheit
Convert an SI conductivity value into the foot-based imperial unit used in US engineering references.
- Note the SI value: record the material's conductivity in W/(m·K).
- Multiply by 0.5777893: this factor yields BTU/(h·ft·°F) directly.
- Confirm the thickness basis: ensure the target reference uses feet, not inches, to avoid a 12× error.
- Worked result: 25 W/(m·K) × 0.5777893 = 14.44473 BTU/(h·ft·°F).
Watts per Metre-Kelvin to BTU per Hour-Foot-Degree Fahrenheit conversion table
| Watts per Metre-Kelvin (W/(m-K)) | BTU per Hour-Foot-Degree Fahrenheit (BTU/(h-ft-°F)) |
|---|---|
| 0 | 0 |
| 1 | 0.5777893 |
| 2 | 1.155579 |
| 3 | 1.733368 |
| 4 | 2.311157 |
| 5 | 2.888947 |
| 6 | 3.466736 |
| 7 | 4.044525 |
| 8 | 4.622315 |
| 9 | 5.200104 |
| 10 | 5.777893 |
| 15 | 8.66684 |
| 20 | 11.55579 |
| 25 | 14.44473 |
| 30 | 17.33368 |
| 40 | 23.11157 |
| 50 | 28.88947 |
| 60 | 34.66736 |
| 70 | 40.44525 |
| 80 | 46.22315 |
| 90 | 52.00104 |
| 100 | 57.77893 |
| 150 | 86.6684 |
| 200 | 115.5579 |
| 250 | 144.4473 |
| 300 | 173.3368 |
| 400 | 231.1157 |
| 500 | 288.8947 |
| 600 | 346.6736 |
| 700 | 404.4525 |
| 800 | 462.2315 |
| 900 | 520.0104 |
| 1000 | 577.7893 |
| 2000 | 1155.579 |
| 3000 | 1733.368 |
| 4000 | 2311.157 |
| 5000 | 2888.947 |
| 10000 | 5777.893 |
| 25000 | 14444.73 |
| 50000 | 28889.47 |
| 100000 | 57778.93 |
| 250000 | 144447.3 |
| 500000 | 288894.7 |
| 1000000 | 577789.3 |
What is the Watt per Metre-Kelvin?
The watt per metre-kelvin is the SI coherent unit of thermal conductivity, quantifying how readily a material conducts heat. It expresses the rate of heat flow through a material per unit thickness for each degree of temperature difference across it.
Definition
A material has a thermal conductivity of one watt per metre-kelvin if a temperature gradient of one kelvin per metre drives a heat flux of one watt per square metre through it:
Because a temperature difference of one kelvin equals one degree Celsius, W/(m·K) and W/(m·°C) are numerically identical.
Origin and History
The unit follows directly from Fourier's law of heat conduction, published by Joseph Fourier in his 1822 Théorie analytique de la chaleur, which states that heat flux is proportional to the negative temperature gradient. The proportionality constant is the thermal conductivity, and it acquired its coherent SI form once the watt, metre and kelvin were established within the International System of Units.
Law and Notable Facts
The watt per metre-kelvin is the standard SI unit for material property tables worldwide. Thermal conductivity spans an enormous range: from aerogels near 0.02 W/(m·K), among the best solid insulators, to diamond at roughly 2000 W/(m·K), the highest of any bulk natural material.
Real-World Examples and Conversions
- Still air conducts heat at about 0.026 W/(m·K); water at about 0.6 W/(m·K).
- Common window glass is near 1.0 W/(m·K); stainless steel about 15 W/(m·K).
- Copper reaches roughly 400 W/(m·K), which is why it is used for heat sinks.
- 1 W/(m·K) = 1000 mW/(m·K) ≈ 0.5778 BTU/(h·ft·°F).
What is the BTU per Hour-Foot-Degree Fahrenheit?
The BTU per hour-foot-degree Fahrenheit is the customary unit of thermal conductivity in the United States and other imperial-using industries. It measures the heat, in British thermal units per hour, conducted through a material one foot thick for each degree Fahrenheit of temperature difference.
Definition
One BTU per hour-foot-degree Fahrenheit corresponds to a heat flow of one BTU per hour through a one-foot thickness for a one-degree-Fahrenheit temperature difference. In coherent SI units:
The exact value depends on the definition of the British thermal unit used; based on the International Table BTU (1055.05585262 J), 1 BTU/(h·ft·°F) = 1.730734666 W/(m·K).
Origin and History
The unit is built from three imperial and customary quantities: the British thermal unit (the heat needed to raise one pound of water by one degree Fahrenheit), the foot, and the Fahrenheit degree. It became the standard for U.S. thermal-property data long before SI was widely adopted and persists in North American engineering practice.
Law and Notable Facts
While the SI watt per metre-kelvin is preferred internationally, BTU/(h·ft·°F) remains entrenched in U.S. mechanical, HVAC and building codes. A useful benchmark: pure copper conducts at about 231 BTU/(h·ft·°F), roughly 400 times better than the fibreglass batts used to insulate walls.
Real-World Examples and Conversions
- Structural steel is about 26 BTU/(h·ft·°F); concrete roughly 0.8–1.0.
- Water conducts at about 0.35 BTU/(h·ft·°F).
- 1 BTU/(h·ft·°F) ≈ 1.7307 W/(m·K) ≈ 1730.7 mW/(m·K).
- Conversely, 1 W/(m·K) ≈ 0.5778 BTU/(h·ft·°F).
Frequently Asked Questions
What is 1 W/(m·K) in BTU/(h·ft·°F)?
One watt per metre-kelvin equals about 0.5777893 BTU/(h·ft·°F). This is the foot-based imperial conductivity unit used in US engineering handbooks.
How does this differ from the BTU-inch form?
This unit measures thickness in feet, while BTU-in/(h·ft²·°F) uses inches; the two differ by a factor of 12, so keep track of which convention a datasheet follows.
How many W/(m·K) is 1 BTU/(h·ft·°F)?
The reverse conversion factor is 1.730735, so one BTU/(h·ft·°F) equals roughly 1.7307 W/(m·K).
Which industries use BTU/(h·ft·°F)?
HVAC design, process and refinery engineering, and pipe/vessel insulation calculations in the US routinely quote thermal conductivity in this unit.
What is 3 W/(m·K) expressed in BTU/(h·ft·°F)?
Multiply 3 by 0.5777893 to get about 1.733368 BTU/(h·ft·°F).
People also convert
Complete Watts per Metre-Kelvin conversion table
| Unit | Result |
|---|---|
| Milliwatts per Metre-Kelvin (mW/(m-K)) | 1000 mW/(m-K) |
| BTU per Hour-Foot-Degree Fahrenheit (BTU/(h-ft-°F)) | 0.5777893 BTU/(h-ft-°F) |
| BTU-Inch per Hour-Square Foot-Degree Fahrenheit (BTU-in/(h-ft2-°F)) | 6.933472 BTU-in/(h-ft2-°F) |
| Calories per Second-Centimetre-Degree Celsius (cal/(s-cm-°C)) | 0.002390057 cal/(s-cm-°C) |