Understanding BTU-Inch per Hour-Square Foot-Degree Fahrenheit to Milliwatts per Metre-Kelvin Conversion
BTU-in/(h·ft²·°F) is the imperial thermal-conductivity unit quoted on insulation, glazing, and building-envelope datasheets. mW/(m·K) is the SI unit scaled to milliwatts, ideal for low-conductivity materials such as foams and aerogels where values fall well below 1 W/(m·K). Converting is essential when matching North American product specs to metric building codes and material databases.
Conversion Formula
To convert BTU-Inch per Hour-Square Foot-Degree Fahrenheit to Milliwatts per Metre-Kelvin, multiply by this factor:
Step-by-Step Example
Convert 25 BTU-Inch per Hour-Square Foot-Degree Fahrenheit to Milliwatts per Metre-Kelvin.
How to Convert BTU-Inch per Hour-Square Foot-Degree Fahrenheit to Milliwatts per Metre-Kelvin
Translate an imperial insulation rating into metric milliwatts per metre-kelvin.
- Take the imperial value: Start with conductivity in BTU-in/(h·ft²·°F).
- Multiply by 144.2279: This gives the equivalent in mW/(m·K).
- Compare with datasheets: Typical insulation lands near 20–40 mW/(m·K).
- Report the result: mW/(m·K).
BTU-Inch per Hour-Square Foot-Degree Fahrenheit to Milliwatts per Metre-Kelvin conversion table
| BTU-Inch per Hour-Square Foot-Degree Fahrenheit (BTU-in/(h-ft2-°F)) | Milliwatts per Metre-Kelvin (mW/(m-K)) |
|---|---|
| 0 | 0 |
| 1 | 144.2279 |
| 2 | 288.4558 |
| 3 | 432.6837 |
| 4 | 576.9116 |
| 5 | 721.1394 |
| 6 | 865.3673 |
| 7 | 1009.595 |
| 8 | 1153.823 |
| 9 | 1298.051 |
| 10 | 1442.279 |
| 15 | 2163.418 |
| 20 | 2884.558 |
| 25 | 3605.697 |
| 30 | 4326.837 |
| 40 | 5769.116 |
| 50 | 7211.394 |
| 60 | 8653.673 |
| 70 | 10095.95 |
| 80 | 11538.23 |
| 90 | 12980.51 |
| 100 | 14422.79 |
| 150 | 21634.18 |
| 200 | 28845.58 |
| 250 | 36056.97 |
| 300 | 43268.37 |
| 400 | 57691.16 |
| 500 | 72113.94 |
| 600 | 86536.73 |
| 700 | 100959.5 |
| 800 | 115382.3 |
| 900 | 129805.1 |
| 1000 | 144227.9 |
| 2000 | 288455.8 |
| 3000 | 432683.7 |
| 4000 | 576911.6 |
| 5000 | 721139.4 |
| 10000 | 1442279 |
| 25000 | 3605697 |
| 50000 | 7211394 |
| 100000 | 14422790 |
| 250000 | 36056970 |
| 500000 | 72113940 |
| 1000000 | 144227900 |
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).
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).
Frequently Asked Questions
How many milliwatts per metre-kelvin is one BTU-in/(h·ft²·°F)?
One BTU-in/(h·ft²·°F) equals 144.2279 mW/(m·K).
How do I convert back to the imperial unit?
Multiply the mW/(m·K) value by 0.006933472 to return to BTU-in/(h·ft²·°F).
Why use milliwatts rather than watts per metre-kelvin?
Insulation materials often have conductivities around 20–40 mW/(m·K), so milliwatts give convenient whole-number values instead of small decimals.
How does this help compare insulation products?
It lets you place an imperial-rated product directly alongside metric-rated foams and aerogels in a single mW/(m·K) column.
What is 25 BTU-in/(h·ft²·°F) in mW/(m·K)?
25 BTU-in/(h·ft²·°F) equals 3605.698 mW/(m·K).
People also convert
Complete BTU-Inch per Hour-Square Foot-Degree Fahrenheit conversion table
| Unit | Result |
|---|---|
| Watts per Metre-Kelvin (W/(m-K)) | 0.1442279 W/(m-K) |
| Milliwatts per Metre-Kelvin (mW/(m-K)) | 144.2279 mW/(m-K) |
| BTU per Hour-Foot-Degree Fahrenheit (BTU/(h-ft-°F)) | 0.08333333 BTU/(h-ft-°F) |
| Calories per Second-Centimetre-Degree Celsius (cal/(s-cm-°C)) | 0.0003447129 cal/(s-cm-°C) |