Wet Bulb Heat Stress Calculator
Calculates wet-bulb temperature — a more honest indicator of heat danger than the heat index.
Inputs
Result
A natural placement between the calculator and the explanation.
What this solves — and what it doesn't
The ‘heat index’ you see on weather apps assumes you’re in shade with some wind. The wet-bulb globe temperature (WBGT) is what occupational safety, military, and athletic training use to decide when to cancel outdoor work. It combines natural wet-bulb temperature (the lowest your skin can cool to by sweating), air temperature, and solar radiation. A WBGT above 32 C means even fit, acclimatized people at rest are at risk of heat illness.
How to read the result
The result is WBGT in C plus a band:
- <27.7 C Normal — full activity
- 27.7 to 29.4 C Caution — water breaks every 30 min
- 29.4 to 31.0 C Extreme Caution — limit to 50% of normal workload
- 31.0 to 32.2 C Danger — non-essential work canceled
- >32.2 C Extreme Danger — cancel all outdoor activity
Wind reduces effective WBGT slightly; we apply a small correction above 10 km/h.
Limitations
- Doesn’t model solar radiation directly (we approximate it in the WBGT formula).
- Doesn’t account for individual acclimatization.
- Stull wet-bulb approximation has ~1 C error vs. psychrometric calculations.
Frequently asked questions
Why not use the heat index?
Heat index assumes shade; WBGT accounts for sun, wind, and humidity together. WBGT is the safer metric for outdoor work.
Does acclimatization help?
Yes — 2 weeks of progressive exposure raises the safe WBGT by 2 to 3 C. Until then, treat yourself as "non-acclimatized."
What about humidity in desert?
Low humidity makes heat index bearable but WBGT can still be elevated. WBGT is more honest in dry heat.