Understanding BTU-Inch per Hour-Square Foot-Degree Fahrenheit to Watts per Metre-Kelvin Conversion
BTU-in/(h·ft²·°F) is the imperial thermal-conductivity unit on North American insulation and building-material datasheets. W/(m·K) is the SI unit of thermal conductivity, the global standard used in material databases, physics, and metric building codes. Converting BTU-in/(h·ft²·°F) to W/(m·K) is the most common thermal-conductivity conversion when moving between imperial product specs and international engineering.
Conversion Formula
To convert BTU-Inch per Hour-Square Foot-Degree Fahrenheit to Watts per Metre-Kelvin, multiply by this factor:
Step-by-Step Example
Convert 25 BTU-Inch per Hour-Square Foot-Degree Fahrenheit to Watts per Metre-Kelvin.
How to Convert BTU-Inch per Hour-Square Foot-Degree Fahrenheit to Watts per Metre-Kelvin
Move an imperial insulation conductivity into the SI standard with a single factor.
- Note the imperial value: Start with conductivity in BTU-in/(h·ft²·°F).
- Multiply by 0.1442279: This yields the SI value in W/(m·K).
- Sanity-check the scale: Insulation values typically land near 0.02–0.04 W/(m·K).
- Report the result: W/(m·K).
BTU-Inch per Hour-Square Foot-Degree Fahrenheit to Watts per Metre-Kelvin conversion table
| BTU-Inch per Hour-Square Foot-Degree Fahrenheit (BTU-in/(h-ft2-°F)) | Watts per Metre-Kelvin (W/(m-K)) |
|---|---|
| 0 | 0 |
| 1 | 0.1442279 |
| 2 | 0.2884558 |
| 3 | 0.4326837 |
| 4 | 0.5769116 |
| 5 | 0.7211394 |
| 6 | 0.8653673 |
| 7 | 1.009595 |
| 8 | 1.153823 |
| 9 | 1.298051 |
| 10 | 1.442279 |
| 15 | 2.163418 |
| 20 | 2.884558 |
| 25 | 3.605697 |
| 30 | 4.326837 |
| 40 | 5.769116 |
| 50 | 7.211394 |
| 60 | 8.653673 |
| 70 | 10.09595 |
| 80 | 11.53823 |
| 90 | 12.98051 |
| 100 | 14.42279 |
| 150 | 21.63418 |
| 200 | 28.84558 |
| 250 | 36.05697 |
| 300 | 43.26837 |
| 400 | 57.69116 |
| 500 | 72.11394 |
| 600 | 86.53673 |
| 700 | 100.9595 |
| 800 | 115.3823 |
| 900 | 129.8051 |
| 1000 | 144.2279 |
| 2000 | 288.4558 |
| 3000 | 432.6837 |
| 4000 | 576.9116 |
| 5000 | 721.1394 |
| 10000 | 1442.279 |
| 25000 | 3605.697 |
| 50000 | 7211.394 |
| 100000 | 14422.79 |
| 250000 | 36056.97 |
| 500000 | 72113.94 |
| 1000000 | 144227.9 |
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 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).
Frequently Asked Questions
How many watts per metre-kelvin is one BTU-in/(h·ft²·°F)?
One BTU-in/(h·ft²·°F) equals 0.1442279 W/(m·K).
How do I convert W/(m·K) back to the imperial unit?
Multiply the W/(m·K) value by 6.933472 to return to BTU-in/(h·ft²·°F).
Why is W/(m·K) the preferred unit?
It is the SI unit of thermal conductivity and appears in essentially all international material databases and engineering standards.
Where is this conversion used most?
Building scientists and HVAC engineers use it to compare U.S. insulation R-values and product specs against metric conductivity data.
What is 25 BTU-in/(h·ft²·°F) in W/(m·K)?
25 BTU-in/(h·ft²·°F) equals 3.605698 W/(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) |