Thermal conductivity is a fundamental material property that quantifies a substance's ability to conduct heat. In engineering, two primary systems are frequently encountered: the Imperial system and the International System of Units (SI).
BTU/(hr·ft·°F): This unit is standard in the United States, representing the heat flow in British Thermal Units per hour through a material one foot thick with a temperature difference of one degree Fahrenheit. It is widely used in HVAC design and building insulation specifications.
W/(m·K): The SI unit, Watts per meter-Kelvin, measures heat flow in Watts through a material one meter thick with a temperature difference of one Kelvin.
The conversion factor is derived from the relationship between the constituent units: \(1 \text{ BTU} \approx 1055.06 \text{ J}\), \(1 \text{ ft} = 0.3048 \text{ m}\), and a temperature interval of \(1 \text{ °F} = 5/9 \text{ K}\). Combining these yields the conversion factor of \(1.730735\).
BTU per hour-foot-Fahrenheit to Watt per meter-Kelvin Conversion Reference Table
BTU per hour-foot-Fahrenheit (BTU/(hr·ft·°F))
Watt per meter-Kelvin (W/(m·K))
0.1
0.1731
0.5
0.8654
1.0
1.7307
2.0
3.4615
5.0
8.6537
10.0
17.3073
20.0
34.6147
50.0
86.5367
100.0
173.0735
500.0
865.3675
1000.0
1730.735
Conversion Example
To convert a thermal conductivity value from Imperial to SI units, multiply the value by the conversion factor of 1.730735.
Because a temperature interval of 1 degree Fahrenheit is smaller than a 1 Kelvin interval. Since 180 degrees Fahrenheit spans the same range as 100 Kelvin, the ratio is 100/180, which simplifies to 5/9.
Yes. Because thermal conductivity measures a temperature gradient (a difference), the magnitude of a degree Fahrenheit is identical to the magnitude of a degree Rankine. Therefore, the conversion factor remains the same.
"On fait la science avec des faits, comme on fait une maison avec des pierres ; mais une accumulation de faits n'est pas plus une science qu'un tas de pierres n'est une maison." "Science is built up of facts, as a house is built of stones; but an accumulation of facts is no more a science than a heap of stones is a house." — Henri Poincaré (French Mathematician, Theoretical Physicist & Mining Engineer)