Understanding BTU-Inch per Hour-Square Foot-Degree Fahrenheit to BTU per Hour-Foot-Degree Fahrenheit Conversion
BTU-in/(h·ft²·°F) is an imperial thermal-conductivity unit expressing heat flow through a one-inch-thick slab, standard on insulation and building-material datasheets. BTU/(h·ft·°F) is the same physical quantity expressed with a one-foot thickness basis, favoured in heavy process and piping engineering. Converting between them just changes the length basis from inches to feet, dividing by 12.
Conversion Formula
To convert BTU-Inch per Hour-Square Foot-Degree Fahrenheit to BTU per Hour-Foot-Degree Fahrenheit, multiply by this factor:
Step-by-Step Example
Convert 25 BTU-Inch per Hour-Square Foot-Degree Fahrenheit to BTU per Hour-Foot-Degree Fahrenheit.
How to Convert BTU-Inch per Hour-Square Foot-Degree Fahrenheit to BTU per Hour-Foot-Degree Fahrenheit
Rebasing from an inch to a foot of thickness is a simple division by 12.
- Take the inch-basis value: Start with conductivity in BTU-in/(h·ft²·°F).
- Multiply by 0.08333333: Equivalent to dividing by 12 to switch to a per-foot basis.
- Confirm the shrink: The foot-basis number should be twelve times smaller.
- Report the result: BTU/(h·ft·°F).
BTU-Inch per Hour-Square Foot-Degree Fahrenheit to BTU per Hour-Foot-Degree Fahrenheit conversion table
| BTU-Inch per Hour-Square Foot-Degree Fahrenheit (BTU-in/(h-ft2-°F)) | BTU per Hour-Foot-Degree Fahrenheit (BTU/(h-ft-°F)) |
|---|---|
| 0 | 0 |
| 1 | 0.08333333 |
| 2 | 0.1666667 |
| 3 | 0.25 |
| 4 | 0.3333333 |
| 5 | 0.4166667 |
| 6 | 0.5 |
| 7 | 0.5833333 |
| 8 | 0.6666667 |
| 9 | 0.75 |
| 10 | 0.8333333 |
| 15 | 1.25 |
| 20 | 1.666667 |
| 25 | 2.083333 |
| 30 | 2.5 |
| 40 | 3.333333 |
| 50 | 4.166667 |
| 60 | 5 |
| 70 | 5.833333 |
| 80 | 6.666667 |
| 90 | 7.5 |
| 100 | 8.333333 |
| 150 | 12.5 |
| 200 | 16.66667 |
| 250 | 20.83333 |
| 300 | 25 |
| 400 | 33.33333 |
| 500 | 41.66667 |
| 600 | 50 |
| 700 | 58.33333 |
| 800 | 66.66667 |
| 900 | 75 |
| 1000 | 83.33333 |
| 2000 | 166.6667 |
| 3000 | 250 |
| 4000 | 333.3333 |
| 5000 | 416.6667 |
| 10000 | 833.3333 |
| 25000 | 2083.333 |
| 50000 | 4166.667 |
| 100000 | 8333.333 |
| 250000 | 20833.33 |
| 500000 | 41666.67 |
| 1000000 | 83333.33 |
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 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).
Frequently Asked Questions
Why is the factor exactly 1/12?
The two units differ only in the thickness basis — inches versus feet — and since one foot is 12 inches, converting requires dividing by 12, giving 0.08333333.
How do I convert back to the inch-basis unit?
Multiply BTU/(h·ft·°F) by 12 to return to BTU-in/(h·ft²·°F).
Are these two units measuring the same physical property?
Yes, both express thermal conductivity; they simply report it per inch or per foot of material thickness.
Which unit do insulation datasheets typically use?
North American insulation and gypsum products usually quote BTU-in/(h·ft²·°F) because material thickness is specified in inches.
What is 25 in the inch-basis unit as foot-basis?
25 BTU-in/(h·ft²·°F) equals 2.083333 BTU/(h·ft·°F).
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) |