What this calculator does
The Wet Bulb Calculator estimates the wet bulb temperature — the lowest temperature to which air can be cooled by evaporating water into it — from the ordinary air temperature and the relative humidity. The wet bulb temperature combines heat and humidity into a single number and is the best simple indicator of how stressful hot, humid conditions are for the human body, because it reflects how well sweat can evaporate and cool you down.
The calculator also shows the approximate dew point and a heat-stress warning level. It runs entirely in your browser and is available in English, Arabic, and Spanish.
How to use the Wet Bulb Calculator
- Enter the air temperature and choose Celsius or Fahrenheit.
- Enter the relative humidity as a percentage from 0 to 100.
- Click "Calculate" to see the wet bulb temperature, the approximate dew point, and a heat-stress advisory.
Formulas
The calculator uses the Stull (2011) approximation for the wet bulb temperature, valid for ordinary surface-weather conditions (RH between 5% and 99%, air temperature between −20 °C and 50 °C):
Results are shown in the unit you chose as well as in Celsius. The dew point is an independent Magnus-formula estimate and agrees closely with the wet bulb calculation over the Stull validity range.
Examples
- A hot, dry afternoon: 40 °C and 15% humidity gives a wet bulb of about 21 °C — uncomfortable but safe for most people.
- A humid summer day: 32 °C and 70% humidity gives a wet bulb of about 27.5 °C — dangerous heat stress; outdoor work should be limited.
- The same 32 °C at 35% humidity gives a wet bulb of only about 21.5 °C, showing why humidity, not just temperature, determines danger.
- Imperial: 95 °F and 60% humidity → wet bulb ≈ 83 °F (28.5 °C) — extreme heat stress.
Heat-stress levels
- Below 18 °C (64 °F) wet bulb — normal conditions; sweat cools the body effectively.
- 18–23 °C (64–73 °F) — caution during prolonged exertion; rest in the shade and drink water.
- 23–28 °C (73–82 °F) — high risk; hard outdoor work and sport should be reduced or rescheduled.
- Above 28 °C (82 °F) — extreme danger; the body can barely cool itself, and even fit people in shade can suffer heatstroke within hours. Sustained wet bulb temperatures above about 31 °C are considered unsurvivable without cooling.
Frequently asked questions
What is the wet bulb temperature?
It is the temperature a thermometer reads when its bulb is covered by a wet wick and air is passed over it. Evaporation of the water cools the bulb, and the drier the air, the more it cools. It is always equal to or lower than the dry air temperature and equal to or higher than the dew point.
Why is wet bulb temperature more important than ordinary temperature?
Because the human body cools itself by sweating, and sweating only works when moisture can evaporate. In humid air, evaporation slows down, so the wet bulb temperature — which captures both heat and humidity — is a much better measure of heat stress than temperature alone. A person cannot survive prolonged exposure to a wet bulb temperature above about 35 °C (95 °F), even in the shade with plenty of water.
How accurate is this calculator?
The Stull formula is accurate to within about ±1 °C over its valid range (RH 5–99%, T from −20 °C to 50 °C), which is sufficient for safety decisions and general weather interpretation. It is not suitable for the upper atmosphere or for lab-grade psychrometrics.
What is the difference between wet bulb temperature and wet bulb globe temperature (WBGT)?
WBGT additionally accounts for solar radiation and wind using a black globe thermometer, and is the standard for industrial and sports heat-safety rules. This calculator gives the simpler wet bulb temperature, which is the main input to many WBGT estimates.
Where is wet bulb temperature used?
Meteorology, HVAC design (cooling towers and evaporative coolers are rated by approach to wet bulb), aviation (wet bulb affects takeoff performance), agriculture, and occupational health limits for work in the heat.
Is my data saved or sent anywhere?
No. Every calculation runs in your browser, and nothing you type is stored or sent to a server.
Related calculators
Other free calculators commonly used with this tool: Cooling Load Calculator, Heat Pump Calculator, and Water Pressure Pump Calculator.
Want a deeper walkthrough? Read our wet bulb temperature guide.