Calculate body heat loss, surface area, or temperature difference from any 2 inputs with unit options in W, kW, BTU/hr, m², sq ft, and °C/°F.
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Body Heat Loss Formula
The calculator uses a simplified body heat loss relationship based on surface area, temperature difference, and a constant of 5.67 × 10^-8. It can solve for heat loss, surface area, or temperature difference when you enter the other two values.
- Q = body heat loss, in watts (W)
- A = surface area, in square meters (m²)
- ΔT = temperature difference, in degrees Celsius (°C)
- 5.67e-8 = constant used by the calculator
The calculator first converts your entered units into base units: watts, square meters, and degrees Celsius. It then applies the matching formula depending on which field is left blank. After calculating the missing value, it converts the answer back into the unit selected for that field.
- To calculate heat loss: enter surface area and temperature difference.
- To calculate surface area: enter heat loss and temperature difference.
- To calculate temperature difference: enter heat loss and surface area.
Unit Conversions Used by the Calculator
| Quantity | Unit | Conversion to base unit | Base unit |
|---|---|---|---|
| Heat loss | W | 1 W = 1 W | W |
| Heat loss | kW | 1 kW = 1000 W | W |
| Heat loss | BTU/hr | 1 BTU/hr = 0.293071 W | W |
| Surface area | sq ft | 1 sq ft = 0.092903 m² | m² |
| Surface area | sq yd | 1 sq yd = 0.836127 m² | m² |
| Temperature difference | °F difference | 1 °F difference = 5/9 °C difference | °C |
Typical Adult Body Surface Area Reference
| Person size | Approximate body surface area | Equivalent in square feet |
|---|---|---|
| Smaller adult | 1.5 m² | 16.1 sq ft |
| Average adult | 1.7 to 1.9 m² | 18.3 to 20.5 sq ft |
| Larger adult | 2.0 to 2.3 m² | 21.5 to 24.8 sq ft |
Example Calculations
Example 1: Calculate heat loss
You enter a surface area of 1.8 m² and a temperature difference of 12°C.
The calculated heat loss is 0.0000012247 W, which the calculator displays rounded according to the selected output unit.
Example 2: Calculate surface area
You enter a heat loss of 0.000002 W and a temperature difference of 20°C.
The required surface area is 1.7637 m².
FAQs
Why do I need to enter exactly two values?
The calculator has three variables: heat loss, surface area, and temperature difference. One value must be unknown so the calculator knows what to solve for. If you enter all three values, there is nothing missing to calculate. If you enter fewer than two values, there is not enough information to solve the formula.
Is a Fahrenheit temperature difference converted the same way as a Fahrenheit temperature reading?
No. This calculator treats the input as a temperature difference, not an absolute temperature reading. A difference of 1°F equals a difference of 5/9°C. Because it is a difference, you do not subtract 32 during the conversion.
Why is the result very small?
The formula used here multiplies by 5.67 × 10^-8, which is a very small constant. That can produce very small heat loss values when using ordinary body surface areas and temperature differences. If you are estimating real human heat loss, remember that actual heat transfer also depends on clothing, air movement, humidity, evaporation, radiation, and metabolic heat production.
