Understanding BTU-Inch per Hour-Square Foot-Degree Fahrenheit to Calories per Second-Centimetre-Degree Celsius Conversion
BTU-in/(h·ft²·°F) is the imperial thermal-conductivity unit found on building-insulation datasheets, based on an inch-thick slab. cal/(s·cm·°C) is a CGS thermal-conductivity unit still seen in older materials-science and physics literature. Converting between them lets engineers reconcile imperial building specs with legacy CGS conductivity tables.
Conversion Formula
To convert BTU-Inch per Hour-Square Foot-Degree Fahrenheit to Calories per Second-Centimetre-Degree Celsius, multiply by this factor:
Step-by-Step Example
Convert 25 BTU-Inch per Hour-Square Foot-Degree Fahrenheit to Calories per Second-Centimetre-Degree Celsius.
How to Convert BTU-Inch per Hour-Square Foot-Degree Fahrenheit to Calories per Second-Centimetre-Degree Celsius
Bridge an imperial insulation conductivity into legacy CGS units with one multiplication.
- Start with the imperial value: Note conductivity in BTU-in/(h·ft²·°F).
- Multiply by 0.0003447129: This yields calories per second-centimetre-degree Celsius.
- Keep enough decimals: The small factor makes precision matter for further calculations.
- Report the result: cal/(s·cm·°C).
BTU-Inch per Hour-Square Foot-Degree Fahrenheit to Calories per Second-Centimetre-Degree Celsius conversion table
| BTU-Inch per Hour-Square Foot-Degree Fahrenheit (BTU-in/(h-ft2-°F)) | Calories per Second-Centimetre-Degree Celsius (cal/(s-cm-°C)) |
|---|---|
| 0 | 0 |
| 1 | 0.0003447129 |
| 2 | 0.0006894259 |
| 3 | 0.001034139 |
| 4 | 0.001378852 |
| 5 | 0.001723565 |
| 6 | 0.002068278 |
| 7 | 0.00241299 |
| 8 | 0.002757703 |
| 9 | 0.003102416 |
| 10 | 0.003447129 |
| 15 | 0.005170694 |
| 20 | 0.006894259 |
| 25 | 0.008617823 |
| 30 | 0.01034139 |
| 40 | 0.01378852 |
| 50 | 0.01723565 |
| 60 | 0.02068278 |
| 70 | 0.0241299 |
| 80 | 0.02757703 |
| 90 | 0.03102416 |
| 100 | 0.03447129 |
| 150 | 0.05170694 |
| 200 | 0.06894259 |
| 250 | 0.08617823 |
| 300 | 0.1034139 |
| 400 | 0.1378852 |
| 500 | 0.1723565 |
| 600 | 0.2068278 |
| 700 | 0.241299 |
| 800 | 0.2757703 |
| 900 | 0.3102416 |
| 1000 | 0.3447129 |
| 2000 | 0.6894259 |
| 3000 | 1.034139 |
| 4000 | 1.378852 |
| 5000 | 1.723565 |
| 10000 | 3.447129 |
| 25000 | 8.617823 |
| 50000 | 17.23565 |
| 100000 | 34.47129 |
| 250000 | 86.17823 |
| 500000 | 172.3565 |
| 1000000 | 344.7129 |
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 Calorie per Second-Centimetre-Degree Celsius?
The calorie per second-centimetre-degree Celsius is the CGS-based unit of thermal conductivity, historically common in physics and physical-chemistry literature. It measures the heat in calories flowing per second through a one-centimetre thickness for each degree Celsius of temperature difference.
Definition
One calorie per second-centimetre-degree Celsius represents a heat flow of one calorie per second through a one-centimetre cube per degree Celsius across it. Using the thermochemical calorie (4.184 J):
The value follows from 4.184 J/s per (0.01 m · 1 K) = 4.184 ÷ 0.01 = 418.4 W/(m·K). If the International Table calorie (4.1868 J) is used instead, the factor is 418.68 W/(m·K).
Origin and History
The unit arose in the CGS era, when heat was measured in calories, lengths in centimetres and temperature in degrees Celsius. It appears throughout older thermal-conductivity tables and heat-transfer texts, especially in chemistry and metallurgy, before the watt per metre-kelvin became standard.
Law and Notable Facts
Though largely superseded by SI, the unit is still encountered in legacy data and some scientific traditions. Its large size is convenient for metals: because 1 cal/(s·cm·°C) equals 418.4 W/(m·K), even highly conductive copper is under 1 in these units, whereas most materials are small fractions.
Real-World Examples and Conversions
- Copper conducts at about 0.94 cal/(s·cm·°C), i.e. roughly 400 W/(m·K).
- Iron is about 0.18 cal/(s·cm·°C).
- Water is roughly 0.0014 cal/(s·cm·°C).
- 1 cal/(s·cm·°C) = 418.4 W/(m·K); conversely 1 W/(m·K) ≈ 0.00239 cal/(s·cm·°C).
Frequently Asked Questions
How many cal/(s·cm·°C) equal one BTU-in/(h·ft²·°F)?
One BTU-in/(h·ft²·°F) equals about 0.0003447129 cal/(s·cm·°C).
How do I convert back to the imperial unit?
Multiply the CGS value by 2900.965 to return to BTU-in/(h·ft²·°F).
Why does the CGS unit still appear in references?
Many classic thermal-property tables from mid-20th-century physics and metallurgy were compiled in CGS units, so conversion is needed to use them with modern imperial specs.
Is cal here the thermochemical or IT calorie?
This conversion uses the calorie consistent with the standard thermal-conductivity definitions; the factor 0.0003447129 already bakes in that choice.
What is 25 BTU-in/(h·ft²·°F) in CGS units?
25 BTU-in/(h·ft²·°F) equals 0.008617823 cal/(s·cm·°C).
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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) |