Heat Index / WBGT Calculator
Calculate heat index and wet bulb globe temperature for exercise safety.
About Heat Index / WBGT Calculator
Humidity impairs evaporative cooling, which is why the apparent temperature exceeds the air temperature. WBGT is preferred for exercise decisions because it includes solar radiation and wind, which the heat index ignores. Heat illness can develop rapidly and unacclimatised participants are at much higher risk, which is why guidance thresholds are set conservatively.
Formula
Heat Index / WBGT
Heat index is the Rothfusz regression on temperature and humidity; WBGT adds sun and wind
- heat index
- Apparent temperature accounting for humidity in the shade
- WBGT
- Wet bulb globe temperature, which also accounts for radiant heat and wind
Worked example
With the default values below, Heat Index / WBGT Calculator returns Heat Index of 33.88. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Air temperatureaccepts -10–55 C
- 30 C
- Relative humidityaccepts 0–100 %
- 65 %
- In direct sunlightone of Yes, No
- Yes
- Wind speedminimum 0 km/h
- 8 km/h
Results
- Heat Index
- 33.88 C
- Estimated WBGT
- 26.41 C
- Heat Index
- 93.0 F
- Heat Risk Category
- Moderate
- Activity Guidance
- Normal activity with usual hydration
Step by step
- 1Values used
- 2Heat Index / WBGT
- 3Heat Index= 33.88 C
- 4Estimated WBGT= 26.41 C
- 5Heat Index= 93.0 F
- 6Heat Risk Category= Moderate
- 7Activity Guidance= Normal activity with usual hydration
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
- These figures are population-average estimates for training and recreational planning only and are not medical advice. Individual responses vary widely. Consult a qualified health professional before starting or significantly changing an exercise, supplement or nutrition programme, particularly if you have any medical condition. Heat illness is a medical emergency. If someone becomes confused, stops sweating, or collapses in the heat, call emergency services and begin cooling immediately. Follow the heat policy of your sport's governing body.
- This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
These figures are population-average estimates for training and recreational planning only and are not medical advice. Individual responses vary widely. Consult a qualified health professional before starting or significantly changing an exercise, supplement or nutrition programme, particularly if you have any medical condition. Heat illness is a medical emergency. If someone becomes confused, stops sweating, or collapses in the heat, call emergency services and begin cooling immediately. Follow the heat policy of your sport's governing body.
Frequently Asked Questions
How is Heat Index / WBGT calculated?
Heat index is the Rothfusz regression on temperature and humidity; WBGT adds sun and wind Humidity impairs evaporative cooling, which is why the apparent temperature exceeds the air temperature. WBGT is preferred for exercise decisions because it includes solar radiation and wind, which the heat index ignores.
Why does Heat Index / WBGT matter?
Heat illness can develop rapidly and unacclimatised participants are at much higher risk, which is why guidance thresholds are set conservatively.
What values do I need to enter?
This calculator takes 4 inputs: Air temperature, Relative humidity, In direct sunlight, Wind speed. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.