What is Wet Bulb Globe Temperature?

On hot days, most of us pay attention to the heat index—a familiar measure that combines air temperature and humidity to reflect how hot it feels. But when it comes to making decisions that affect safety, performance, or working conditions, the heat index isn't always enough. Enter Wet Bulb Globe Temperature (WBGT)—a more comprehensive and scientifically grounded way to evaluate environmental heat stress.

WBGT goes beyond temperature and humidity. It accounts for wind speed, solar radiation, and sun angle—factors that significantly impact how the human body experiences heat, especially during physical exertion. In high-stakes environments where health and performance are on the line, WBGT provides a clearer picture.

Whether on a construction site, in a military training camp, or during a sports practice, WBGT is the gold standard for heat safety. Unlike the heat index, which assumes shady, low-activity conditions, WBGT reflects real-world environments—under the sun, in motion, and subject to changing weather patterns. Organizations like OSHA, the U.S. military, and major athletic associations rely on it to reduce risk and keep people safe.

This guide explores WBGT, how it's used, and why it matters. By understanding and integrating WBGT into your safety protocols, you're not just improving comfort—you're actively protecting lives.

What is WBGT?

WBGT isn't as well-known as the heat index, but it provides a far more nuanced and reliable measure of heat stress in real-world conditions. Unlike the heat index, which estimates perceived temperature based on air temperature and humidity in shaded environments, WBGT captures the full spectrum of environmental variables contributing to heat-related strain on the human body.

WBGT measurements are taken in direct sunlight and include temperature, humidity, wind speed, sun angle, and cloud cover—collectively referred to as solar radiation. This integration of atmospheric and radiant heat factors allows WBGT to present a realistic snapshot of what it feels like to exert oneself under current environmental conditions.

Because WBGT factors in radiation and wind, it is especially useful in outdoor scenarios where heat stress is not just about how hot it is, but how the heat behaves. For instance, a day with moderate temperatures but intense sun and minimal wind can result in a high WBGT reading, signaling a significant risk of heat illness even when the air temperature seems manageable. This situational accuracy is essential for athletes, construction workers, military personnel, and anyone spending extended time outdoors.

Furthermore, WBGT can account for differences in terrain and geography. Urban heat islands, open fields, shaded forests, and coastal areas all have unique heat dynamics that influence how bodies respond to physical activity. With WBGT, safety professionals gain the precision necessary to tailor guidance to specific microclimates, ensuring safety protocols match on-the-ground realities.

This broader, integrated approach to heat stress makes WBGT the preferred method in policy, prevention, and field application. It's not just a number—it's actionable insight into human thermal strain.

Wet Bulb Globe Temperature vs Heat Index

Signs of Heat Stress & Illness

The signs of heat stress should be monitored closely at the earliest stages to prevent serious illness or injury. Even healthy young people can experience a heat stroke given the right conditions. Typical signs of heat illness and stress include:

• Dizziness
• Confusion
• Nausea
• Heavy sweating
• Pale and clammy skin
• Skin may be cold to the touch
• Weakness
• Headache
• Heat cramps
• Losing consciousness

WBGT & Environmental Monitoring

WBGT is the preferred method for monitoring heat stress whether it's for work, competitive sports, recreational activities, or training and conditioning.

How will WBGT Protect People from Exertional Heat Stress Better than Heat Index?

Heat safety starts with monitoring the conditions. WBGT monitoring is the most effective first step in preventing exertional heat stress illness for athletes, military members, and workers in high-risk environments. By continuously evaluating real-time environmental data, teams can make informed decisions that adapt to shifting weather conditions and activity levels.

The Kestrel 5400 Heat Stress Tracker automatically calculates accurate WBGT using on-site environmental inputs rather than relying on estimates or off-site reports, allowing for a truly location-specific heat risk assessment. The 5400 is used by safety professionals in major sports organizations such as the NFL, MLS, and USTA, as well as by all branches of the U.S. Military, demonstrating its reliability and credibility in both civilian and defense sectors.

WBGT & Athletics

When establishing WBGT guidelines for physical activity, it's critical to understand that acclimatization plays a major role in how individuals respond to heat. What may be considered manageable conditions for one person can be dangerous for another, depending largely on geographic location and past exposure. For example, an athlete training regularly in the heat and humidity of Louisiana is likely more physiologically adapted to those conditions than a counterpart from a cooler northern state like Maine. Thus, 90°F might feel routine in one setting but oppressive and dangerous in another.

These regional differences highlight the importance of using WBGT thresholds that are flexible and customized to local climate norms and populations. Standardized WBGT readings offer a benchmark, but best practices require localized guidelines that account for both environmental and human factors. Athletic trainers and safety officers should consult regional climatological data, adjust activity intensity and duration accordingly, and educate participants on recognizing signs of heat-related illness before conditions become dangerous. WBGT makes it possible to craft these context-aware responses, ensuring not just blanket safety protocols, but more precise, situationally appropriate safeguards.

Athletic Safety Chart

A safety chart is useful in many situations when determining the correct action to take in correlation with the WBGT reading. Developing an action plan for preventing heat illness is dependent on the region. Some areas of the country are more susceptible to causing heat illness at different times of the year.

Developing an action plan for preventing heat illness is dependent on the region. Some areas of the country are more susceptible to causing heat illness at different times of the year.

WBGT Monitoring for Heat Safety

• WBGT has been shown to provide an accurate measure of environmental heat stress.
• WBGT can be used as a preventive measure during exercise in the heat by making activity modifications as WBGT rises.
• When developing guidelines for activity modification using WBGT, it is necessary to include: work/rest ratios, length of activity, hydration breaks, equipment to be worn (if applicable), and a level at which activity is canceled.
• WBGT guidelines must be region-specific since temperatures fluctuate differently by region. People's response to exercising in the heat may vary depending on the area where their usual exercise sessions occur.
• WBGT modifications should be fluid, meaning that if conditions become more restrictive during the day or a particular practice, modifications should be more restrictive. As environmental conditions become milder, modifications should be less restrictive.

WBGT & Military Training

Heat stress can quickly become a dangerous and critical problem if not taken seriously. Through WBGT monitoring, leaders can obtain real-time updates on their work environment conditions, allowing them to act accordingly before things become potentially life-threatening. The United States Military uses WBGT to modify basic training during hot conditions. The chart below shows the modifications that are used during basic training. 

WBGT & Occupational Heat Safety

Heat-related illnesses can be deadly, yet they remain one of the most overlooked safety hazards in the workplace. Occupational heat stress frequently affects employees working in extreme or strenuous conditions. Therefore, understanding how to recognize and address heat-related health concerns is vital for employers seeking to create a safe work environment.

Every year, countless workers around the world suffer heat-related illnesses and injuries, putting their health, well-being, and livelihoods at risk. That's why the Occupational Safety and Health Administration (OSHA) launched its National Emphasis Program (NEP) for Heat-Related Hazards to raise awareness of this serious issue.

The program aims to prevent workplace heat stress by educating employers about risks associated with overexposure to high temperatures and how they can keep their employees safe and healthy during hot working conditions. In addition, OSHA will initiate inspections on heat priority days. The NEP defines a heat priority day as one where employees are exposed to outdoor heat at or above 80°F with humidity at or above 40 percent. Employers should expect increased inspections for targeted industries at both outdoor and indoor job sites.

WBGT is the most accurate tool for measuring heat hazards for outdoor and indoor workers where radiant heat sources are a factor. Monitoring the WBGT conditions where workers are present is key to preventing serious illness and injury.

The American Conference of Governmental Industrial Hygienists (ACGIH) provides guidance for maintaining awareness about when workers may be exposed to heat stress so that preventive measures can be taken.

Kestrel 5400 Heat Stress Trackers for WBGT Monitoring

Monitoring WBGT is straightforward and dependable with Kestrel weather meters, making them an essential tool for safety managers, athletic trainers, and field professionals. These devices are designed for real-world use—rugged, accurate, and easy to deploy across diverse environments. With a Kestrel weather meter on site, you can make informed decisions about work-rest cycles, hydration timing, and training duration based on live WBGT data rather than assumptions or general forecasts.

This level of insight allows teams to stay ahead of dangerous conditions by adjusting their heat safety protocols in real time. Whether managing construction crews under a blazing sun or coordinating a youth sports tournament in peak summer, the ability to continuously monitor WBGT helps ensure that responses remain flexible. From mid-day peaks to cooler evenings, Kestrel Heat Stress Trackers give you the confidence to act decisively, protect your people, and maintain operational momentum without compromising safety.

FAQs About WBGT and Heat Stress

What makes WBGT more accurate than the heat index?

The heat index only considers temperature and humidity in shady conditions. WBGT incorporates sunlight, wind speed, and radiant heat, offering a more realistic view of how environmental conditions affect the human body, particularly during exertion.

How often should WBGT readings be taken?

In high-heat environments, readings should be taken hourly or more frequently during peak heat times. Continuous monitoring using devices like the Kestrel 5400 ensures up-to-the-minute data to guide safe practices.

Can WBGT be used indoors?

Yes. WBGT is especially useful in industrial environments where radiant heat from machinery or poor ventilation can increase stress on the body. Monitoring both indoor and outdoor conditions can help establish safe working conditions across various settings.

Who sets WBGT guidelines for athletes and workers?

Organizations like the Korey Stringer Institute, ACGIH, and OSHA provide frameworks and recommendations. However, guidelines should be customized to the region, industry, and level of physical activity involved.

What equipment is required to measure WBGT?

A WBGT-enabled weather meter such as the Kestrel 5400 is ideal. It automatically accounts for the various environmental factors contributing to WBGT and displays real-time readings for use in policy and safety decision-making.

Are there laws requiring WBGT monitoring?

While OSHA has not mandated WBGT monitoring nationally, it encourages it as part of its Heat Illness Prevention campaign. Some states, such as California, have specific heat illness prevention requirements, including environmental monitoring.

How does WBGT factor into emergency response plans?

Organizations use WBGT data to trigger heat alerts, modify schedules, and activate cooling stations or medical readiness protocols. It is a foundational piece in any heat-related emergency response system.

What's the difference between WBGT and a regular thermometer reading?

A regular thermometer only tells you the ambient air temperature. WBGT, by contrast, accounts for multiple environmental factors, including solar radiation, wind speed, and humidity. This makes it far more relevant for assessing heat stress risk, especially during exertion or in full sun.

Can WBGT help guide hydration schedules?

Yes. WBGT readings can inform appropriate hydration intervals, particularly for athletes and workers in high-heat settings. The higher the WBGT, the more frequent and proactive hydration breaks should be to reduce the risk of heat illness and maintain performance.

Is WBGT useful in cold climates?

While WBGT is primarily used to assess heat stress, it can also provide valuable data in transitional climates where warm weather spikes occur. Sudden heat waves can catch individuals off guard, even in colder regions, making WBGT monitoring a proactive safety tool.

How do employers implement WBGT into workplace safety plans?

Employers can incorporate WBGT data into job hazard assessments, safety briefings, and daily work/rest schedules. Posting WBGT readings on-site and training staff to interpret them fosters shared accountability for heat safety.

What types of environments benefit most from WBGT monitoring?

WBGT monitoring can benefit any setting where heat, humidity, sunlight, and physical activity converge. This includes construction sites, agriculture, military installations, athletic fields, warehouses, manufacturing floors, and emergency response zones.

How can WBGT data be shared with teams in the field?

Devices like the Kestrel 5400 with LiNK™ technology allow wireless data sharing to smartphones or tablets. This ensures supervisors, coaches, and medical teams can view live conditions and respond promptly across large sites or dispersed teams.

For unbeatable accuracy, easy operation, and reliable readings, rely on Kestrel Heat Stress Trackers for WBGT readings and heat illness prevention.