Understanding Watts per Metre-Kelvin to BTU-Inch per Hour-Square Foot-Degree Fahrenheit Conversion
The watt per metre-kelvin (W/(m·K)) is the SI unit of thermal conductivity, describing how much heat flows through a material per unit thickness and temperature difference. The BTU-inch per hour-square foot-degree Fahrenheit is the imperial equivalent widely used on North American insulation and building-material datasheets, where thickness is measured in inches. This conversion lets engineers compare European material specs with US R-value and k-value listings.
Conversion Formula
To convert Watts per Metre-Kelvin to BTU-Inch per Hour-Square Foot-Degree Fahrenheit, multiply by this factor:
Step-by-Step Example
Convert 25 Watts per Metre-Kelvin to BTU-Inch per Hour-Square Foot-Degree Fahrenheit.
How to Convert Watts per Metre-Kelvin to BTU-Inch per Hour-Square Foot-Degree Fahrenheit
Translate an SI thermal-conductivity value into the inch-based imperial form used on US insulation specs.
- Read the SI conductivity: take your material's k-value in W/(m·K).
- Multiply by 6.933472: this single factor converts directly to BTU-in/(h·ft²·°F).
- Check units: confirm the target datasheet uses inch thickness, not foot thickness, before comparing.
- Worked result: 25 W/(m·K) × 6.933472 = 173.3368 BTU-in/(h·ft²·°F).
Watts per Metre-Kelvin to BTU-Inch per Hour-Square Foot-Degree Fahrenheit conversion table
| Watts per Metre-Kelvin (W/(m-K)) | BTU-Inch per Hour-Square Foot-Degree Fahrenheit (BTU-in/(h-ft2-°F)) |
|---|---|
| 0 | 0 |
| 1 | 6.933472 |
| 2 | 13.86694 |
| 3 | 20.80042 |
| 4 | 27.73389 |
| 5 | 34.66736 |
| 6 | 41.60083 |
| 7 | 48.5343 |
| 8 | 55.46777 |
| 9 | 62.40125 |
| 10 | 69.33472 |
| 15 | 104.0021 |
| 20 | 138.6694 |
| 25 | 173.3368 |
| 30 | 208.0042 |
| 40 | 277.3389 |
| 50 | 346.6736 |
| 60 | 416.0083 |
| 70 | 485.343 |
| 80 | 554.6777 |
| 90 | 624.0125 |
| 100 | 693.3472 |
| 150 | 1040.021 |
| 200 | 1386.694 |
| 250 | 1733.368 |
| 300 | 2080.042 |
| 400 | 2773.389 |
| 500 | 3466.736 |
| 600 | 4160.083 |
| 700 | 4853.43 |
| 800 | 5546.777 |
| 900 | 6240.125 |
| 1000 | 6933.472 |
| 2000 | 13866.94 |
| 3000 | 20800.42 |
| 4000 | 27733.89 |
| 5000 | 34667.36 |
| 10000 | 69334.72 |
| 25000 | 173336.8 |
| 50000 | 346673.6 |
| 100000 | 693347.2 |
| 250000 | 1733368 |
| 500000 | 3466736 |
| 1000000 | 6933472 |
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-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
What is the conversion factor from W/(m·K) to BTU-in/(h·ft²·°F)?
One watt per metre-kelvin equals about 6.933472 BTU-in/(h·ft²·°F). This imperial form keeps thickness in inches, which is why the factor differs from the per-foot version.
Why does the imperial unit use inches for thickness?
Building insulation in the US is commonly rated per inch of thickness, so BTU-in/(h·ft²·°F) matches how batts, foams and boards are specified on datasheets.
How many W/(m·K) is 1 BTU-in/(h·ft²·°F)?
The reverse factor is about 0.1442279, so one BTU-in/(h·ft²·°F) equals roughly 0.1442 W/(m·K).
Where is this conversion most useful?
It is used when comparing thermal conductivity (k-value) of construction materials between SI datasheets and North American product literature, and when converting to or from R-values.
What is 10 W/(m·K) in BTU-in/(h·ft²·°F)?
Multiply 10 by 6.933472 to get about 69.33472 BTU-in/(h·ft²·°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) |