Understanding BTU per Hour-Foot-Degree Fahrenheit to BTU-Inch per Hour-Square Foot-Degree Fahrenheit Conversion
BTU/(h·ft·°F) expresses thermal conductivity on a per-foot thickness basis, common in process, piping, and heavy-industry engineering. BTU-in/(h·ft²·°F) uses a one-inch thickness basis and is the form printed on building-insulation and glazing datasheets. Converting from the foot basis to the inch basis multiplies by 12, letting industrial figures line up with construction-product specs.
Conversion Formula
To convert BTU per Hour-Foot-Degree Fahrenheit to BTU-Inch per Hour-Square Foot-Degree Fahrenheit, multiply by this factor:
Step-by-Step Example
Convert 25 BTU per Hour-Foot-Degree Fahrenheit to BTU-Inch per Hour-Square Foot-Degree Fahrenheit.
How to Convert BTU per Hour-Foot-Degree Fahrenheit to BTU-Inch per Hour-Square Foot-Degree Fahrenheit
Switching from a foot to an inch thickness basis is a simple multiplication by 12.
- Take the foot-basis value: Start with conductivity in BTU/(h·ft·°F).
- Multiply by 12: This rebases the thickness reference to one inch.
- Confirm the growth: The inch-basis number should be twelve times larger.
- Report the result: BTU-in/(h·ft²·°F).
BTU per Hour-Foot-Degree Fahrenheit to BTU-Inch per Hour-Square Foot-Degree Fahrenheit conversion table
| BTU per Hour-Foot-Degree Fahrenheit (BTU/(h-ft-°F)) | BTU-Inch per Hour-Square Foot-Degree Fahrenheit (BTU-in/(h-ft2-°F)) |
|---|---|
| 0 | 0 |
| 1 | 12 |
| 2 | 24 |
| 3 | 36 |
| 4 | 48 |
| 5 | 60 |
| 6 | 72 |
| 7 | 84 |
| 8 | 96 |
| 9 | 108 |
| 10 | 120 |
| 15 | 180 |
| 20 | 240 |
| 25 | 300 |
| 30 | 360 |
| 40 | 480 |
| 50 | 600 |
| 60 | 720 |
| 70 | 840 |
| 80 | 960 |
| 90 | 1080 |
| 100 | 1200 |
| 150 | 1800 |
| 200 | 2400 |
| 250 | 3000 |
| 300 | 3600 |
| 400 | 4800 |
| 500 | 6000 |
| 600 | 7200 |
| 700 | 8400 |
| 800 | 9600 |
| 900 | 10800 |
| 1000 | 12000 |
| 2000 | 24000 |
| 3000 | 36000 |
| 4000 | 48000 |
| 5000 | 60000 |
| 10000 | 120000 |
| 25000 | 300000 |
| 50000 | 600000 |
| 100000 | 1200000 |
| 250000 | 3000000 |
| 500000 | 6000000 |
| 1000000 | 12000000 |
What is the BTU per Hour-Foot-Degree Fahrenheit?
The BTU per hour-foot-degree Fahrenheit is the customary unit of thermal conductivity in the United States and other imperial-using industries. It measures the heat, in British thermal units per hour, conducted through a material one foot thick for each degree Fahrenheit of temperature difference.
Definition
One BTU per hour-foot-degree Fahrenheit corresponds to a heat flow of one BTU per hour through a one-foot thickness for a one-degree-Fahrenheit temperature difference. In coherent SI units:
The exact value depends on the definition of the British thermal unit used; based on the International Table BTU (1055.05585262 J), 1 BTU/(h·ft·°F) = 1.730734666 W/(m·K).
Origin and History
The unit is built from three imperial and customary quantities: the British thermal unit (the heat needed to raise one pound of water by one degree Fahrenheit), the foot, and the Fahrenheit degree. It became the standard for U.S. thermal-property data long before SI was widely adopted and persists in North American engineering practice.
Law and Notable Facts
While the SI watt per metre-kelvin is preferred internationally, BTU/(h·ft·°F) remains entrenched in U.S. mechanical, HVAC and building codes. A useful benchmark: pure copper conducts at about 231 BTU/(h·ft·°F), roughly 400 times better than the fibreglass batts used to insulate walls.
Real-World Examples and Conversions
- Structural steel is about 26 BTU/(h·ft·°F); concrete roughly 0.8–1.0.
- Water conducts at about 0.35 BTU/(h·ft·°F).
- 1 BTU/(h·ft·°F) ≈ 1.7307 W/(m·K) ≈ 1730.7 mW/(m·K).
- Conversely, 1 W/(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
Why is the factor exactly 12?
The two units differ only in whether thickness is measured in feet or inches, and one foot equals 12 inches, so the foot-basis value is 12 times the inch-basis number.
How do I convert back to the foot-basis unit?
Multiply the inch-basis value by 0.08333333 (that is, divide by 12) to return to BTU/(h·ft·°F).
Do the two units describe the same property?
Yes, both are thermal conductivity; only the reference thickness differs.
When would I need this direction of conversion?
When an industrial spec is given per foot but you need to compare it against insulation datasheets that quote the inch basis.
What is 25 BTU/(h·ft·°F) in the inch-basis unit?
25 BTU/(h·ft·°F) equals 300 BTU-in/(h·ft²·°F).
People also convert
Complete BTU per Hour-Foot-Degree Fahrenheit conversion table
| Unit | Result |
|---|---|
| Watts per Metre-Kelvin (W/(m-K)) | 1.730735 W/(m-K) |
| Milliwatts per Metre-Kelvin (mW/(m-K)) | 1730.735 mW/(m-K) |
| BTU-Inch per Hour-Square Foot-Degree Fahrenheit (BTU-in/(h-ft2-°F)) | 12 BTU-in/(h-ft2-°F) |
| Calories per Second-Centimetre-Degree Celsius (cal/(s-cm-°C)) | 0.004136555 cal/(s-cm-°C) |