Wet Bulb Temperature Calculator
Calculate wet bulb globe temperature (WBGT) and assess heat stress risk levels. This wet bulb calculator uses dry bulb temperature, relative humidity, and atmospheric pressure to determine thermal comfort and safety for outdoor activities, athletes, construction workers, and heat-exposed occupations.
Enter Weather Parameters
No results to display. Please enter parameters and click Calculate.
About Wet Bulb Temperature
What is Wet Bulb Temperature
Wet bulb temperature is the lowest temperature a thermometer can reach when covered with a wet cloth and exposed to air current. It represents the combined effect of temperature and humidity on human thermal comfort and heat stress. Wet bulb temperature is crucial for assessing heat-related illness risk in athletes, outdoor workers, and military personnel.
Understanding Wet Bulb Temperature
The wet bulb temperature measures the cooling effect of evaporation. As moisture evaporates from a wet surface, it absorbs heat, lowering the temperature. In dry conditions, wet bulb temperature is significantly lower than dry bulb temperature. In humid conditions, wet bulb approaches dry bulb temperature, reducing evaporative cooling and increasing heat stress risk.
Key Factors Affecting Wet Bulb Temperature
- Dry bulb temperature: Higher air temperature increases wet bulb temperature
- Relative humidity: Higher humidity reduces evaporative cooling, increasing wet bulb
- Atmospheric pressure: Altitude affects evaporation rate and wet bulb calculation
- Air movement: Wind enhances evaporation, lowering wet bulb temperature
- Radiation: Solar radiation heats the wet surface, affecting measurements
- Clothing: Insulating clothing reduces evaporative cooling effectiveness
- Activity level: Exercise generates metabolic heat, increasing thermal stress
- Acclimatization: Heat-acclimated individuals tolerate higher wet bulb better
Why Wet Bulb Temperature Matters
Wet bulb temperature is the most accurate measure of heat stress on the human body. It determines whether outdoor activities are safe or should be restricted. High wet bulb temperatures indicate conditions where the body cannot cool itself through sweating, risking heat stroke and heat exhaustion. Military forces, athletic organizations, and workplace safety programs use wet bulb thresholds to protect personnel.
How to Use the Wet Bulb Calculator
This calculator uses the Stull formula to estimate wet bulb temperature from easily measured parameters. Enter your weather conditions to quickly determine heat stress level and activity safety.
Step-by-Step Instructions
- 1Measure or obtain the dry bulb temperature in your preferred unit (°C or °F)
- 2Determine the relative humidity percentage (0-100%)
- 3Enter atmospheric pressure if known, otherwise use 1013.25 hPa for sea level
- 4Select the correct temperature unit for your location
- 5Select the atmospheric pressure unit matching your reference
- 6Click Calculate to compute wet bulb temperature
- 7Review the wet bulb temperature result
- 8Check the heat stress level color and description
- 9Read the activity recommendation for your situation
- 10Export results as CSV if needed for record-keeping
Helpful Tips for Accurate Calculations
- Use an aspirated thermometer for accurate dry bulb readings
- Measure humidity with a calibrated hygrometer for accuracy
- Update calculations every 15-30 minutes during heat events
- Account for altitude by using local atmospheric pressure
- Remember that wet bulb is more accurate than heat index for heat stress
- Consider adding 2-3°C for direct sunlight exposure effects
- Use wet bulb temperature thresholds specific to your activity
- Monitor individuals for heat exhaustion symptoms regardless of calculation
- Adjust activity restrictions based on acclimatization status
- Maintain hydration protocols regardless of heat stress level
Applications of Wet Bulb Temperature
Wet bulb temperature is essential for heat safety management in multiple sectors. It provides objective criteria for activity restrictions and medical response protocols.
Athletic Training & Sports
Coaches and athletic trainers use wet bulb temperature to modify practice intensity and duration. Sports organizations establish mandatory protocols for activity restrictions at specific wet bulb thresholds to prevent heat-related illnesses in athletes.
Examples: Practice modifications, fluid replacement protocols, mandatory rest periods, heat illness prevention, athletic competition safety
Military Operations
Military forces use wet bulb temperature to establish combat load restrictions, exercise duration limits, and mandatory rest-recovery cycles for personnel. Heat casualty prevention is critical during field training and operations.
Examples: Training intensity control, combat load management, rest schedules, heat casualty prevention, operational planning
Occupational Safety
Employers in construction, manufacturing, agriculture, and outdoor industries use wet bulb standards to protect worker safety. OSHA and other regulatory bodies reference wet bulb thresholds for workplace safety requirements.
Examples: Work-rest schedules, mandatory hydration breaks, equipment modifications, medical surveillance, hazard communication
Public Health & Emergency Response
Public health agencies use wet bulb forecasts to issue heat warnings and activate cooling center protocols. Emergency responders use wet bulb data for resource planning during heat events.
Examples: Heat warning systems, cooling center activation, vulnerable population outreach, hospital preparedness, emergency coordination
Medical Monitoring
Clinicians and occupational health providers use wet bulb temperature to guide monitoring frequency for heat-exposed workers. Medical surveillance increases when wet bulb exceeds critical thresholds.
Examples: Pre-shift medical screening, vital sign monitoring, heat illness diagnosis, treatment guidance, return-to-work decisions
Research & Analysis
Researchers use wet bulb temperature data to study heat stress physiology, validate safety protocols, and develop improved heat illness prevention strategies.
Examples: Thermal comfort research, safety protocol validation, climate impact assessment, prevention strategy development, occupational health studies
Wet Bulb Temperature Formula
The wet bulb temperature is calculated using approximation formulas based on dry bulb temperature and relative humidity. The Stull formula provides accurate estimates for practical applications.
Stull Approximation Formula
Variable Definitions
- Tw: Wet bulb temperature in °C (result)
- T: Dry bulb temperature in °C
- RH: Relative humidity as percentage (0-100%)
- arctan: Inverse tangent function (in radians)
- sqrt: Square root function
- ^: Exponentiation operator
- Constants: Stull formula empirical coefficients refined for accuracy
- Atmospheric pressure: Used indirectly through altitude adjustment if needed
This calculator also computes heat index using the Rothfusz regression formula for conditions where wet bulb temperature exceeds 26.7°C and humidity exceeds 40%. Wet bulb temperature is the preferred metric for heat stress assessment in occupational and athletic contexts.
Factors Affecting Wet Bulb Temperature
Multiple environmental and physiological factors influence wet bulb temperature and heat stress. Understanding these factors helps optimize activity safety protocols.
Dry Bulb Temperature
The actual air temperature has the most direct impact on wet bulb temperature. As dry bulb temperature increases, wet bulb temperature rises proportionally, increasing heat stress risk. Temperature is measured in Celsius or Fahrenheit.
Relative Humidity
Humidity dramatically affects wet bulb temperature by reducing evaporative cooling effectiveness. High humidity means the air already contains significant moisture, limiting the body's ability to cool through perspiration and sweat evaporation.
Atmospheric Pressure
Atmospheric pressure affects saturation vapor pressure and evaporation rates. Higher pressure at sea level versus high altitude influences how much cooling evaporation can provide, affecting wet bulb calculations and heat stress assessment.
Wind Speed & Air Movement
Air movement enhances evaporative cooling, lowering wet bulb temperature. Still air reduces evaporation, increasing heat stress, while wind can significantly reduce heat stress risk through improved cooling.
Solar Radiation
Direct sunlight adds thermal stress beyond air temperature effects. Clear, sunny conditions increase the actual heat stress experienced, while cloud cover and shade reduce thermal load significantly.
Clothing & Equipment
Insulating clothing and protective equipment reduce evaporative cooling effectiveness. Heavy, waterproof, or tight-fitting clothing traps heat, increasing core body temperature and heat stress risk substantially.
Activity Level & Metabolic Heat
Exercise and work generate internal metabolic heat, adding to environmental heat stress. Higher activity intensity increases heat production, requiring greater evaporative cooling for thermal balance.
Individual Acclimatization
Heat acclimatization improves the body's thermal regulation and heat tolerance. Individuals accustomed to hot conditions can tolerate higher wet bulb temperatures, while unacclimatized individuals face greater heat illness risk.
Frequently Asked Questions
What is the difference between wet bulb and heat index?
Wet bulb temperature measures actual evaporative cooling capacity and is the preferred metric for heat stress assessment in occupational and athletic settings. Heat index combines temperature and humidity but doesn't directly measure cooling effectiveness. Wet bulb is more accurate for determining when activity restrictions are needed.
What wet bulb temperature is considered dangerous?
Generally, wet bulb temperatures above 32°C (90°F) represent extreme danger where even sedentary individuals face severe heat illness risk. Above 28°C (82°F) represents danger for active individuals. Above 24°C (75°F) requires caution for strenuous activities. The exact threshold depends on activity level and individual acclimatization.
How do I measure wet bulb temperature myself?
Measure dry bulb temperature with a regular thermometer and relative humidity with a hygrometer. Use this calculator to compute wet bulb temperature from these measurements. A psychrometer is the traditional instrument for direct wet bulb measurement but is less commonly used now.
Can wet bulb temperature exceed dry bulb temperature?
No, wet bulb temperature is always lower than or equal to dry bulb temperature. It equals dry bulb temperature only when relative humidity is 100% (saturated air). As humidity decreases, the difference between wet bulb and dry bulb increases.
Why does wet bulb matter for outdoor workers?
Wet bulb temperature determines the body's ability to cool itself through sweat evaporation. When wet bulb exceeds the body's cooling capacity, dangerous heat accumulation occurs, risking heat exhaustion and heat stroke. OSHA and workplace safety regulations increasingly use wet bulb thresholds to protect workers.
How often should I recalculate wet bulb during heat events?
Update calculations every 15-30 minutes during heat events or when conditions change significantly. Temperature and humidity fluctuate throughout the day, affecting heat stress risk. Frequent updates ensure current safety protocols match actual conditions.
Is wet bulb temperature used in sports medicine?
Yes, wet bulb temperature is essential in athletic training. Coaches use wet bulb thresholds to modify practice intensity, mandate rest periods, and implement hydration protocols. High school and collegiate sports organizations increasingly adopt wet bulb-based guidelines to prevent heat illnesses.
What does atmospheric pressure do in wet bulb calculations?
Atmospheric pressure affects saturation vapor pressure and evaporation rates. Higher pressure increases the saturation vapor pressure, affecting how much moisture the air can hold. For most practical applications at sea level, using 1013.25 hPa is acceptable.
Can I use this calculator indoors?
Yes, this calculator works for any location where you can measure or know the dry bulb temperature and relative humidity. Indoor spaces with different atmospheric conditions can also be evaluated using actual pressure measurements.
How accurate is the Stull formula used in this calculator?
The Stull formula provides excellent accuracy for practical heat stress assessment in the range of -40°C to 50°C and 0% to 100% relative humidity. For research requiring maximum precision, more complex formulas exist, but Stull provides sufficient accuracy for safety applications.