Wet-Bulb Temperature Calculator
Calculate wet-bulb temperature, dew point, and heat stress danger levels instantly from ambient temperature and relative humidity.
Input Parameters
Step-by-Step Guide: How to Use the Wet-Bulb Calculator
- Enter Ambient Air Temperature: Measure or input the standard dry-bulb air temperature using your thermometer and select either Celsius (°C) or Fahrenheit (°F).
- Input Relative Humidity (%): Enter the relative humidity reading obtained from a hygrometer or weather broadcast.
- Review Thermal Metrics: Click Calculate Wet-Bulb Temp or press Enter to receive the exact wet-bulb value, dew point, wet-bulb depression, and health risk severity level.
Formulas & Calculation Logic
This calculator relies on Stull's Empirical Formula (Roland Stull, 2011), which provides high-precision estimates of wet-bulb temperature ($T_w$) at standard sea-level pressure using dry-bulb temperature ($T$ in °C) and relative humidity ($RH$ in %):
Where all atan (arctan) functions operate in radians. Additionally, the Dew Point ($T_d$) is derived via the Magnus-Tetens approximation:
Understanding Wet-Bulb Temperature: The Universal Metric for Heat Stress
Wet-bulb temperature ($T_w$) is an essential meteorological and physiological metric that measures the lowest temperature air can achieve solely through the evaporative cooling of water. Unlike standard dry-bulb temperature—which simply measures ambient thermal kinetic energy—wet-bulb temperature accounts for how moisture in the atmosphere directly impacts evaporation efficiency.
For humans and warm-blooded animals, evaporative cooling via perspiration is the primary defense mechanism against hyperthermia. When moisture saturates the air (high relative humidity), sweat cannot evaporate efficiently from the skin, preventing core body heat dissipation even if ambient air temperatures seem manageable.
The 35°C (95°F) Human Survival Threshold
Modern physiological research establishes 35°C (95°F) wet-bulb temperature as the absolute theoretical upper limit of human adaptation. At a wet-bulb reading of 35°C, even a healthy individual with unlimited drinking water resting in total shade will experience continuous core body heat accumulation, leading to heatstroke or death within a few hours.
Recent empirical studies show that serious physiological stress and cardiovascular strain begin at much lower thresholds—around 28°C to 31°C wet-bulb temperature—especially during outdoor physical labor or among vulnerable populations such as elderly individuals and children.
Heat Stress Danger Thresholds
| Wet-Bulb Temp (°C) | Wet-Bulb Temp (°F) | Risk Assessment | Recommended Safety Measures |
|---|---|---|---|
| < 22.0 °C | < 71.6 °F | Low Risk / Normal | Standard daily activities; adequate hydration. |
| 22.0 °C – 27.9 °C | 71.6 °F – 82.2 °F | Moderate Caution | Schedule regular rest breaks during strenuous outdoor exertion. |
| 28.0 °C – 30.9 °C | 82.4 °F – 87.6 °F | High Warning | Limit heavy labor; mandate shade and electrolyte replenishment. |
| 31.0 °C – 34.9 °C | 87.8 °F – 94.8 °F | Extreme Danger | High risk of heat stroke; cancel outdoor athletics and physical work. |
| ≥ 35.0 °C | ≥ 95.0 °F | Critical / Lethal Limit | Potentially fatal condition without active air conditioning or cooling. |
Practical Applications across Industries
- Occupational Health & Safety: Construction, mining, and agriculture supervisors utilize wet-bulb readings to enforce mandatory work-rest cycles and prevent occupational heat illness.
- HVAC & Cooling Towers: HVAC engineers calculate wet-bulb temperature to determine the physical cooling limit of evaporative chillers and swamp coolers.
- Agricultural Risk Management: Livestock farmers monitor wet-bulb readings to trigger misting systems and ventilation fans for cattle, poultry, and swine herds.
Frequently Asked Questions (FAQ)
Wet-bulb temperature is the lowest temperature air can reach through evaporative cooling alone under current pressure and humidity conditions. It reflects how effectively sweating cools the human body.
At 35°C wet-bulb temperature, sweat cannot evaporate from human skin to release heat. Metabolic heat builds up continuously, causing hyperthermia even in healthy adults resting in the shade.
Dew point is the temperature at which air reaches saturation and water condenses. Wet-bulb temperature sits between dry-bulb air temperature and dew point, indicating evaporative cooling potential.
This calculator uses Stull's empirical equation, which combines dry-bulb temperature in °C and relative humidity % to compute wet-bulb values accurately at sea level.