How it's calculated
Tw = T·atan(0.151977·√(RH+8.313659)) + atan(T+RH) − atan(RH−1.676331) + 0.00391838·RH^1.5·atan(0.023101·RH) − 4.686035
Tw = wet-bulb temperature (°C), T = air (dry-bulb) temperature in °C, RH = relative humidity in %. Stull (2011) empirical approximation, valid roughly −20 to 50 °C and 5 to 99% RH.
Reference ranges
| Wet bulb temp | What it means |
|---|---|
| Below 26 °C | Generally safe |
| 26-30 °C | Caution, limit exertion |
| 31-34 °C | Dangerous heat stress |
| 35 °C and up | Human survival limit |
Common questions
Why is 35 °C wet bulb the survival limit?
At that point your body can no longer shed heat by sweating, so core temperature climbs even at rest. It is the theoretical limit for human survival.
What range does this formula cover?
The Stull 2011 formula is valid from about -20 to +50 °C and from 5 to 99 percent relative humidity.