Wet-Bulb Temperature Calculator
Estimate the wet-bulb temperature, a measure of heat stress that combines temperature and humidity into the physical floor on evaporative cooling.
Educational estimate, not health advice.
This is an empirical sea-level approximation from temperature and relative humidity. It cannot establish whether conditions are dangerous for you: sun, wind, clothing, workload, acclimatization, age, medication, and existing health conditions are not inputs, and all of them move the line. Use your local heat alerts and WBGT or occupational guidance for decisions, and seek medical care for heat-illness symptoms.
In or above the range where laboratory studies find heat stress becomes uncompensable for young healthy adults. Older adults and people with health conditions reach that point sooner.
Check your local heat alerts and any workplace heat rules that apply to you.
Why Wet-Bulb Temperature Matters
Where the 35°C (95°F) figure comes from: It is a theoretical benchmark from modelling work published in 2010, describing the point at which an idealised resting person in the shade with unlimited water could no longer shed metabolic heat by evaporation. It was never a safety threshold, and it is widely misquoted as one. Laboratory work since 2021 has measured the actual point at which heat stress becomes uncompensable in young healthy adults, and found it substantially lower, roughly 26 to 31°C wet-bulb depending on air temperature and humidity. Older adults and people with health conditions reach it sooner still.
What wet-bulb adds to the heat index: Heat index estimates how hot conditions feel, while wet-bulb temperature describes the physical floor on evaporative cooling. Neither is a verdict on your own safety. Sun, wind, clothing, workload, acclimatization, age, medication, and existing health conditions all move the line, and none of them are inputs here.
Climate Change Impact: Regions that previously never reached dangerous wet-bulb temperatures are now experiencing them more frequently. Parts of South Asia, the Persian Gulf, and the U.S. Gulf Coast are increasingly at risk.
Wet-Bulb Temperature Bands
Rough context only. These bands describe physics, not a person. The wet-bulb value at which heat stress actually becomes uncompensable varies with air temperature, humidity, age, health, and acclimatization, and is not fixed at any of these boundaries.
Evaporative cooling is generally effective for most people.
Heat stress is possible during sustained physical activity.
Approaching the lower end of the measured uncompensable range, which is lowest in hot, dry conditions.
In or above the range where studies find heat stress becomes uncompensable for young healthy adults.
Well above the measured uncompensable range for young healthy adults.
The theoretical benchmark from 2010 modelling work. Measured human limits are lower. Values this high are exceptionally rare.
Understanding Wet-Bulb Temperature
What is Wet-Bulb Temperature?
Wet-bulb temperature is measured by wrapping a wet cloth around a thermometer bulb. As water evaporates, it cools the thermometer. The reading shows the lowest temperature achievable through evaporative cooling - the same mechanism your body uses to sweat.
Wet-Bulb vs. Heat Index
Heat index estimates how hot it feels to the human body, while wet-bulb temperature directly measures how effectively sweat can cool you. At 100% humidity, wet-bulb equals the air temperature because no evaporation can occur - making it feel hotter than the heat index might suggest.
Who is Most at Risk?
Outdoor workers, athletes, older adults, young children, people with cardiovascular or respiratory conditions, and those without air conditioning face the greatest risk. Their limits sit below the values measured in young healthy study participants, which is one reason no single wet-bulb number can define safety for everyone.
Practical Applications
Outdoor Work & Athletics
Military organizations and sports governing bodies set work/rest cycles using WBGT (wet-bulb globe temperature), which is a different measurement: it combines a wet-bulb reading with solar radiation and air temperature. WBGT is the index those guidelines are written against, not the plain wet-bulb value shown here. Check the WBGT guidance that applies to your activity.
HVAC & Building Design
Engineers use wet-bulb temperature to design cooling systems. It determines the efficiency of cooling towers and evaporative coolers, which can only cool air down to the wet-bulb temperature.
Agriculture
Farmers and livestock managers monitor wet-bulb temperature to protect animals from heat stress. Cattle, pigs, and poultry are all vulnerable to dangerous wet-bulb conditions.
Climate Research
Scientists track wet-bulb temperatures globally to understand climate change impacts on human habitability. Some regions may become periodically uninhabitable as wet-bulb temperatures rise.
How is Wet-Bulb Temperature Calculated?
This calculator uses Stull's formula (2011), an empirical approximation at standard sea-level pressure. The published range is -20 to 50°C and 5 to 99% relative humidity, excluding cold, dry combinations. This heat-stress tool deliberately supports only 0 to 50°C (32 to 122°F) to avoid that exception. At exactly 100% humidity it returns the air temperature directly. See the original paper.
The wet-bulb temperature is always equal to or lower than the dry-bulb (regular) temperature. At 100% humidity, they are equal because no evaporative cooling can occur. The greater the difference between dry-bulb and wet-bulb temperatures, the more effective sweating will be at cooling you.
Note: True wet-bulb temperature also depends on atmospheric pressure, which this calculator assumes to be at sea level (1013.25 hPa). At higher altitudes, actual wet-bulb temperatures may differ slightly.
Experience All Features
Download WeatherAI free and explore. Upgrade to Standard or Pro to unlock advanced features.
Free to download • No credit card required
More on Heat Stress
Heat safety guides and calculators for training, working, and playing in the heat.
Tool
Heat Index Calculator
Calculate how hot it really feels when humidity is part of the story.
Guide
The Heat Index Explained
How temperature and humidity combine into a 'feels like' temperature, and how to stay safe in extreme heat.
Tool
Dew Point Calculator
Convert between temperature, humidity, and dew point for planning and forecasting.
Use Case
Weather App for Runners
Time runs around heat, humidity, and air quality with hour-by-hour conditions.