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Wet Bulb Temperature Calculator

Enter the air temperature and the relative humidity.

°C
%

From 5% to 99%.

This result is an estimate only. Double-check important figures before relying on them.

How it is calculated

  • Stull’s empirical formula uses the air temperature T (°C) and relative humidity RH (%)
  • Wet bulb ≈ 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

For how it feels to you, use the heat index calculator.

Worked example

Air at 32 °C with 70% humidity:

  • Wet bulb temperature is about 27 °C

Why your number may differ

The formula is an approximation and assumes normal sea-level pressure. Heat safety advice should follow official sources, not this estimate alone.

Frequently asked questions

What is the wet bulb temperature?

The temperature a wet surface cools to as water evaporates from it. It combines heat and humidity, and is lower than the air temperature unless the air is saturated.

Why does it matter for heat stress?

The body cools by sweating, which depends on evaporation. When the wet bulb temperature is very high, sweat evaporates poorly and heat is dangerous.

How accurate is the formula?

Stull’s formula is within about 1 °C for ordinary air, from −20 to 50 °C and 5% to 99% humidity.

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