Wet Bulb Temperature Calculator

The wet bulb temperature is the lowest temperature air can reach by evaporating water into it. It equals the reading of a thermometer wrapped in a wet cloth and fanned with air.

It uses the Stull 2011 empirical fit, which estimates the wet bulb temperature directly from air temperature in Celsius and relative humidity at standard sea-level pressure.

The body cools by sweating, which is evaporation. A wet bulb near 35 C means sweat cannot cool you, so sustained wet bulb temperatures that high are dangerous even to healthy people.

At 100 percent humidity the wet bulb equals the air temperature because no more water can evaporate. As humidity falls, more evaporation is possible and the wet bulb drops further below the air temperature.

It is within a few tenths of a degree across normal conditions, roughly -20 to 50 C and 5 to 99 percent humidity. It assumes standard pressure, so high altitudes shift the result slightly.