Understanding Milliwatts per Metre-Kelvin to BTU-Inch per Hour-Square Foot-Degree Fahrenheit Conversion
The milliwatt per metre-kelvin (mW/(m·K)) is a metric measure of thermal conductivity, describing how many milliwatts of heat flow through a one-metre thickness of material per kelvin of temperature difference; it is convenient for insulators and low-conductivity materials. The BTU-inch per hour-square foot-degree Fahrenheit is the imperial R-value companion unit widely used in the US building and insulation industry, expressing heat flow through a one-inch-thick, one-square-foot slab. This conversion lets engineers translate lab-reported metric conductivities into the imperial figures printed on insulation datasheets.
Conversion Formula
To convert Milliwatts per Metre-Kelvin to BTU-Inch per Hour-Square Foot-Degree Fahrenheit, multiply by this factor:
Step-by-Step Example
Convert 25 Milliwatts per Metre-Kelvin to BTU-Inch per Hour-Square Foot-Degree Fahrenheit.
How to Convert Milliwatts per Metre-Kelvin to BTU-Inch per Hour-Square Foot-Degree Fahrenheit
Translate a metric thermal-conductivity value into the imperial insulation unit with one multiplication.
- Recall the factor: One mW/(m·K) equals 0.006933472 BTU-in/(h·ft²·°F).
- Start with your value: Note the conductivity in milliwatts per metre-kelvin.
- Multiply: Multiply that value by 0.006933472 to get the imperial figure.
- Result: For 25 mW/(m·K), the result is 25 × 0.006933472 = 0.173337 BTU-in/(h·ft²·°F).
Milliwatts per Metre-Kelvin to BTU-Inch per Hour-Square Foot-Degree Fahrenheit conversion table
| Milliwatts per Metre-Kelvin (mW/(m-K)) | BTU-Inch per Hour-Square Foot-Degree Fahrenheit (BTU-in/(h-ft2-°F)) |
|---|---|
| 0 | 0 |
| 1 | 0.006933472 |
| 2 | 0.01386694 |
| 3 | 0.02080042 |
| 4 | 0.02773389 |
| 5 | 0.03466736 |
| 6 | 0.04160083 |
| 7 | 0.0485343 |
| 8 | 0.05546777 |
| 9 | 0.06240125 |
| 10 | 0.06933472 |
| 15 | 0.1040021 |
| 20 | 0.1386694 |
| 25 | 0.1733368 |
| 30 | 0.2080042 |
| 40 | 0.2773389 |
| 50 | 0.3466736 |
| 60 | 0.4160083 |
| 70 | 0.485343 |
| 80 | 0.5546777 |
| 90 | 0.6240125 |
| 100 | 0.6933472 |
| 150 | 1.040021 |
| 200 | 1.386694 |
| 250 | 1.733368 |
| 300 | 2.080042 |
| 400 | 2.773389 |
| 500 | 3.466736 |
| 600 | 4.160083 |
| 700 | 4.85343 |
| 800 | 5.546777 |
| 900 | 6.240125 |
| 1000 | 6.933472 |
| 2000 | 13.86694 |
| 3000 | 20.80042 |
| 4000 | 27.73389 |
| 5000 | 34.66736 |
| 10000 | 69.33472 |
| 25000 | 173.3368 |
| 50000 | 346.6736 |
| 100000 | 693.3472 |
| 250000 | 1733.368 |
| 500000 | 3466.736 |
| 1000000 | 6933.472 |
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-Inch per Hour-Square Foot-Degree Fahrenheit?
The BTU-inch per hour-square foot-degree Fahrenheit is the unit of thermal conductivity most commonly used for building and insulation materials in the United States. It states the heat, in BTU per hour, conducted through one square foot of a material one inch thick per degree Fahrenheit of temperature difference.
Definition
The unit uses inch thickness and square-foot area rather than foot thickness, making it exactly one twelfth of the BTU per hour-foot-degree Fahrenheit:
Based on the International Table BTU, the exact value is 0.144227889 W/(m·K), i.e. 1.730734666 ÷ 12.
Origin and History
Insulation and building products are thin sheets or boards, so engineers found it natural to express conductivity per inch of thickness across a square foot of area. This "k-value" convention became the North American standard for insulation datasheets and is the basis of the R-value system, where R = thickness (inches) ÷ k-value.
Law and Notable Facts
The unit underpins U.S. insulation labelling. The R-value printed on insulation is derived from this conductivity: a lower k-value in BTU·in/(h·ft²·°F) yields a higher R-value per inch, meaning better insulation. Typical fibreglass batt has a k-value near 0.25–0.30.
Real-World Examples and Conversions
- Rigid polyisocyanurate foam has a k-value of about 0.14 BTU·in/(h·ft²·°F), giving roughly R-7 per inch.
- Softwood lumber is about 0.8 BTU·in/(h·ft²·°F).
- 1 BTU·in/(h·ft²·°F) ≈ 0.14423 W/(m·K) ≈ 144.23 mW/(m·K).
- Because it is 1/12 of BTU/(h·ft·°F), 12 BTU·in/(h·ft²·°F) = 1 BTU/(h·ft·°F).
Frequently Asked Questions
How many BTU-in/(h·ft²·°F) equal one milliwatt per metre-kelvin?
One milliwatt per metre-kelvin equals about 0.006933472 BTU-in/(h·ft²·°F), so metric conductivities in milliwatts translate to small imperial values.
How do I convert milliwatts per metre-kelvin to this imperial unit?
Multiply the mW/(m·K) value by 0.006933472. For example, 25 mW/(m·K) becomes 0.173337 BTU-in/(h·ft²·°F).
Where is the BTU-inch conductivity unit used?
It is the standard unit behind insulation R-values and U-factors in the US construction industry, describing heat flow through a one-inch-thick material sample.
How many milliwatts per metre-kelvin equal one BTU-in/(h·ft²·°F)?
The reverse factor is about 144.2279 mW/(m·K) per BTU-in/(h·ft²·°F).
Why is thermal conductivity important for insulation?
Lower thermal conductivity means a material resists heat flow better, which is why insulation products advertise low mW/(m·K) values or, equivalently, low BTU-inch conductivities.
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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) |