Wet Bulb Calculator
Find the wet-bulb temperature from air temperature and humidity — or enter a dry-bulb and wet-bulb pair from a sling psychrometer to get relative humidity. Pressure- and elevation-aware.
Two ways to use this calculator
If you know temperature and humidity: set Calculate to a mode that takes air temperature (Relative Humidity or Dew Point), enter your values, and read the Wet-Bulb Temperature in the results.
If you have a sling psychrometer: choose “Relative Humidity (I know dry bulb + wet bulb)” and enter both thermometer readings to get relative humidity, dew point, and the full psychrometric state.
What is wet-bulb temperature?
Wet-bulb temperature is the lowest temperature you can reach purely by evaporating water into the air. Wrap a thermometer bulb in a wet wick, swing it through the air, and evaporation pulls heat away until it settles at the wet-bulb temperature. In dry air, lots of water can evaporate and the reading drops far below the actual (dry-bulb) temperature. In saturated air, nothing evaporates and the two readings match.
Why wet-bulb temperature matters
Your body cools itself the same way the wet wick does — by evaporating sweat. That makes the wet-bulb temperature the real yardstick for heat stress. A sustained wet-bulb of 35°C (95°F) is considered the theoretical limit of human survival: beyond it, sweat cannot evaporate and body temperature climbs no matter how much you rest or drink. Serious danger begins well before that, so athletes, the military, and industrial safety programs track wet-bulb globe temperature closely.
How it's calculated
The calculator solves the psychrometer equation, which balances the air's actual vapor pressure against the evaporative cooling term A × P × (T − T_wb). Because there is no simple algebraic solution, it uses a numerical search to find the wet-bulb temperature where both sides agree — and it recomputes atmospheric pressure from your elevation, since thinner air evaporates moisture differently.
Go deeper with Wet Bulb vs Dry Bulb Temperature: The Survival Threshold Explained and How to Read a Psychrometric Chart.
Frequently Asked Questions
- What is wet-bulb temperature?
- Wet-bulb temperature is the lowest temperature air can reach by evaporating water into it. It is what a thermometer wrapped in a wet wick reads in moving air. Because it captures both heat and humidity, it is the true measure of evaporative cooling and heat stress.
- What is the 35°C (95°F) wet-bulb survival limit?
- A sustained wet-bulb temperature of 35°C (95°F) is widely cited as the theoretical limit of human survival. At that point sweat can no longer evaporate to cool the body, so core temperature rises even for a healthy person resting in the shade. Dangerous heat stress begins well below this, around a 28–31°C wet-bulb.
- How is wet-bulb temperature calculated?
- This calculator solves the psychrometer equation, which balances the air's actual vapor pressure against the cooling from evaporation. It searches for the wet-bulb value that makes both sides agree, and it adjusts for atmospheric pressure when you enter an elevation.
- What is the difference between wet-bulb and dry-bulb temperature?
- Dry-bulb temperature is ordinary air temperature measured by a standard thermometer. Wet-bulb temperature is measured with a wetted wick and is always equal to or lower than the dry-bulb. The two are only equal at 100% relative humidity, when no more evaporation is possible.
- Does elevation affect wet-bulb temperature?
- Yes. Lower atmospheric pressure at altitude changes the rate of evaporation, so the calculator lets you enter elevation in feet to refine the wet-bulb and other psychrometric outputs.