About this tool
The Wet-Bulb Temperature Calculator estimates the wet-bulb temperature (Tw) — the temperature a parcel of air would reach if cooled to saturation by evaporating water into it at constant pressure. It is the reading a thermometer wrapped in a wet wick shows in a moving airstream, and it sets the hard physical limit on how much cooling sweat or a swamp cooler can deliver. A sustained wet-bulb near 35°C is considered the survivability threshold for humans.
This tool uses the Stull (2011) empirical formula: 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, with temperature T in °C, relative humidity RH in %, and the arctangents evaluated in radians. It is accurate to within a few tenths of a degree near standard sea-level pressure (1013.25 hPa) for RH between 5% and 99% and T from −20°C to 50°C.
Everything runs locally in your browser — no data leaves the page. Enter the air temperature (°C or °F) and relative humidity; the result is shown in both °C and °F along with the wet-bulb depression (the gap between dry-bulb and wet-bulb temperature), which widens as the air gets drier. Accuracy degrades at high altitude or far from standard pressure.