Understanding Milliwatts per Metre-Kelvin to BTU per Hour-Foot-Degree Fahrenheit Conversion
The milliwatt per metre-kelvin (mW/(m·K)) expresses thermal conductivity in SI-derived terms, giving heat flow in milliwatts through a metre thickness per kelvin difference. The BTU per hour-foot-degree Fahrenheit is the imperial thermal-conductivity unit used by US engineers, based on a one-foot thickness rather than the one-inch basis of insulation R-values. Converting between them is common when comparing material data reported in metric literature against imperial handbooks for pipes, walls, and heat exchangers.
Conversion Formula
To convert Milliwatts per Metre-Kelvin to BTU per Hour-Foot-Degree Fahrenheit, multiply by this factor:
Step-by-Step Example
Convert 25 Milliwatts per Metre-Kelvin to BTU per Hour-Foot-Degree Fahrenheit.
How to Convert Milliwatts per Metre-Kelvin to BTU per Hour-Foot-Degree Fahrenheit
Move from the metric conductivity unit to the imperial foot-based unit in one step.
- Recall the factor: One mW/(m·K) equals 0.0005777893 BTU/(h·ft·°F).
- Take your value: Note the conductivity in milliwatts per metre-kelvin.
- Multiply: Multiply that value by 0.0005777893 to reach BTU/(h·ft·°F).
- Result: For 25 mW/(m·K), the result is 25 × 0.0005777893 = 0.0144447 BTU/(h·ft·°F).
Milliwatts per Metre-Kelvin to BTU per Hour-Foot-Degree Fahrenheit conversion table
| Milliwatts per Metre-Kelvin (mW/(m-K)) | BTU per Hour-Foot-Degree Fahrenheit (BTU/(h-ft-°F)) |
|---|---|
| 0 | 0 |
| 1 | 0.0005777893 |
| 2 | 0.001155579 |
| 3 | 0.001733368 |
| 4 | 0.002311157 |
| 5 | 0.002888947 |
| 6 | 0.003466736 |
| 7 | 0.004044525 |
| 8 | 0.004622315 |
| 9 | 0.005200104 |
| 10 | 0.005777893 |
| 15 | 0.00866684 |
| 20 | 0.01155579 |
| 25 | 0.01444473 |
| 30 | 0.01733368 |
| 40 | 0.02311157 |
| 50 | 0.02888947 |
| 60 | 0.03466736 |
| 70 | 0.04044525 |
| 80 | 0.04622315 |
| 90 | 0.05200104 |
| 100 | 0.05777893 |
| 150 | 0.0866684 |
| 200 | 0.1155579 |
| 250 | 0.1444473 |
| 300 | 0.1733368 |
| 400 | 0.2311157 |
| 500 | 0.2888947 |
| 600 | 0.3466736 |
| 700 | 0.4044525 |
| 800 | 0.4622315 |
| 900 | 0.5200104 |
| 1000 | 0.5777893 |
| 2000 | 1.155579 |
| 3000 | 1.733368 |
| 4000 | 2.311157 |
| 5000 | 2.888947 |
| 10000 | 5.777893 |
| 25000 | 14.44473 |
| 50000 | 28.88947 |
| 100000 | 57.77893 |
| 250000 | 144.4473 |
| 500000 | 288.8947 |
| 1000000 | 577.7893 |
What is the Milliwatt per Metre-Kelvin?
The milliwatt per metre-kelvin is a unit of thermal conductivity equal to one thousandth of a watt per metre-kelvin. Its convenient scale makes it the preferred unit for describing thermal insulators and gases, whose conductivities are small fractions of a watt per metre-kelvin.
Definition
One milliwatt per metre-kelvin is 10⁻³ watt per metre-kelvin, the SI unit of thermal conductivity:
Like its parent unit, it may equivalently be written mW/(m·°C), since a one-kelvin interval equals a one-degree-Celsius interval.
Origin and History
The unit is simply the SI watt per metre-kelvin scaled by the standard milli- prefix (10⁻³). It became common in the insulation, cryogenics and gas-property literature during the twentieth century, where reporting figures such as 26 mW/(m·K) for air is clearer than 0.026 W/(m·K).
Law and Notable Facts
The milliwatt per metre-kelvin is a coherent SI unit with a decimal prefix and is legal for use worldwide. Building-insulation performance is often stated in mW/(m·K): the lower the value, the better the insulator, which is why manufacturers compete to push products below 30 mW/(m·K).
Real-World Examples and Conversions
- Dry air at room temperature conducts heat at about 26 mW/(m·K).
- Mineral wool and glass-fibre insulation typically fall between 30 and 40 mW/(m·K).
- Polyurethane foam boards reach roughly 22–25 mW/(m·K).
- 1 mW/(m·K) = 0.001 W/(m·K); conversely 1 W/(m·K) = 1000 mW/(m·K).
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
How many BTU/(h·ft·°F) equal one milliwatt per metre-kelvin?
One milliwatt per metre-kelvin equals about 0.0005777893 BTU/(h·ft·°F), a small value because the imperial unit uses a full-foot thickness basis.
How do I convert mW/(m·K) to BTU/(h·ft·°F)?
Multiply the milliwatt-per-metre-kelvin value by 0.0005777893. For example, 25 mW/(m·K) equals 0.0144447 BTU/(h·ft·°F).
What is the difference between this unit and the BTU-inch unit?
The BTU/(h·ft·°F) unit uses a one-foot thickness, while BTU-in/(h·ft²·°F) uses a one-inch thickness; the foot-based value is exactly twelve times smaller for the same material.
How many milliwatts per metre-kelvin equal one BTU/(h·ft·°F)?
The reverse factor is about 1730.735 mW/(m·K) per BTU/(h·ft·°F).
Where is this imperial conductivity unit applied?
Engineers use BTU/(h·ft·°F) for heat-transfer calculations on piping, insulation, and process equipment where imperial units remain standard, such as in US chemical and HVAC design.
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Complete Milliwatts per Metre-Kelvin conversion table
| Unit | Result |
|---|---|
| Watts per Metre-Kelvin (W/(m-K)) | 0.001 W/(m-K) |
| BTU per Hour-Foot-Degree Fahrenheit (BTU/(h-ft-°F)) | 0.0005777893 BTU/(h-ft-°F) |
| BTU-Inch per Hour-Square Foot-Degree Fahrenheit (BTU-in/(h-ft2-°F)) | 0.006933472 BTU-in/(h-ft2-°F) |
| Calories per Second-Centimetre-Degree Celsius (cal/(s-cm-°C)) | 0.000002390057 cal/(s-cm-°C) |