Foundational explainer
Wet Bulb Globe Temperature, or WBGT, is an environmental heat-stress metric. It helps describe how hot conditions may feel to the body when temperature, humidity, sunlight, radiant heat, and wind are considered together.
That matters because people do not experience heat through air temperature alone. A humid day can make sweating less effective. A sunny field can add radiant heat. A breezy location may allow more cooling than a sheltered one. A paved worksite, rooftop, or artificial turf field can feel different from a shaded grass area even when the air temperature is the same.
WBGT is widely used in heat-safety planning for outdoor work, athletics, military training, events, and other settings where heat exposure and physical activity matter. It is useful because it connects the weather environment more directly to heat stress than air temperature alone.
Key takeaways
- WBGT is an environmental heat-stress metric, not a measure of body temperature.
- It combines temperature, humidity, radiant heat, and wind more directly than air temperature alone.
- Measured, estimated, and forecast WBGT each support different kinds of decisions.
- WBGT always needs context such as workload, clothing, acclimatization, and policy.
Important note
WBGT is not a direct measure of body temperature, and it does not determine whether a specific person is safe. It should be used as one input alongside workload, clothing, acclimatization, health status, policy, supervision, and professional judgment.
What WBGT measures
WBGT combines several environmental factors that affect the body’s ability to gain and lose heat.
Air temperature
Air temperature is the familiar dry-bulb temperature reported in most weather forecasts. It matters, but by itself it does not capture humidity, sun, wind, or radiant heat.
Humidity and evaporation
Sweating cools the body when sweat evaporates from the skin. When humidity is high, evaporation becomes less effective. Sweat may drip from the skin without providing as much cooling.
This is one reason WBGT can be concerning even when air temperature alone does not look extreme.
Radiant heat and sunlight
Radiant heat comes from the sun and from hot surfaces such as pavement, roofs, vehicles, machinery, buildings, and athletic fields. Direct sun can raise heat stress even when the air temperature is the same as a shaded location.
Wind and air movement
Air movement can help move heat and moisture away from the body. A breezy open field may allow more cooling than a sheltered courtyard, sideline, or work area where buildings, trees, equipment, or terrain block airflow.
Wind does not eliminate heat risk, especially during heavy exertion or when clothing and equipment limit cooling.
The three standard WBGT components
A standard WBGT measurement uses three temperature sensors. Each sensor captures a different part of the heat environment.
Natural wet bulb temperature
Natural wet bulb temperature reflects humidity, air movement, and evaporative cooling. It is closely tied to how well sweat can evaporate from the skin.
Black globe temperature
Black globe temperature reflects radiant heat. It captures the influence of direct sun and other radiant heat sources, such as hot surfaces, machinery, or nearby structures.
Dry bulb temperature
Dry bulb temperature is regular air temperature measured without adjustment for humidity, sun, or wind.
Together, these components provide a more complete picture of environmental heat stress than air temperature alone.
The standard WBGT formulas
WBGT is calculated differently depending on whether there is solar load.
For outdoor environments with direct sun or meaningful solar load:
WBGT = 0.7 × natural wet bulb temperature + 0.2 × black globe temperature + 0.1 × dry bulb temperature
For indoor settings or outdoor shade without solar load:
WBGT = 0.7 × natural wet bulb temperature + 0.3 × black globe temperature
These formulas show why humidity and evaporation matter so much. Natural wet bulb temperature receives the largest weight. The black globe term is also important because radiant heat can substantially change heat stress in sun-exposed or hot-surface environments.
Measured, estimated, and forecast WBGT
WBGT can come from different sources. The right source depends on the decision.
Measured WBGT
Measured WBGT comes from an onsite WBGT meter. This is the most direct way to assess conditions at a specific work area, field, sideline, event site, or training location.
Onsite measurement is especially important when a policy, rule, or standard requires it.
Estimated WBGT
Estimated WBGT uses weather observations or model data to calculate WBGT when direct measurement is not available. This can be useful for broader monitoring and planning, but the estimate depends on how well the weather data represent the actual site.
A nearby weather station may not capture artificial turf, asphalt, a rooftop, a shaded courtyard, a wind-blocked work area, or radiant heat from local surfaces.
Forecast WBGT
Forecast WBGT estimates how WBGT may change over the next several hours or days. Forecasts are useful because many heat-safety decisions happen before the hottest part of the day.
Forecast WBGT supports planning. It does not replace onsite measurement when onsite measurement is required by a workplace, athletic association, school, military unit, event plan, or other policy.
WBGT and heat index are not the same
Heat index combines air temperature and humidity. It is familiar and useful for general public weather awareness, especially for hot and humid conditions.
WBGT includes more of the outdoor heat environment: temperature, humidity, radiant heat, and wind. That makes it especially useful when the decision involves exertion, direct sun, equipment, long exposure, or scheduling.
Heat index is not inherently bad, and WBGT is not automatically better for every purpose. The better metric depends on the decision. For general public messaging, heat index may be easier to recognize. For planning outdoor work, sports, camps, events, or training, WBGT often provides more relevant information.
For a shorter comparison, see Heat Index vs WBGT.
What WBGT does not include
WBGT describes the environment. It does not include every factor that affects heat strain in a person or group.
- how hard someone is working or exercising,
- whether a person is heat-acclimatized,
- whether clothing, uniforms, pads, PPE, or equipment limit cooling,
- whether a person recently had illness, poor sleep, or dehydration,
- whether someone is taking medication that affects heat tolerance,
- whether someone has a health condition that changes risk,
- whether shade, cooling, water, or recovery space is available,
- whether trained staff or medical support are present,
- what workplace, school, athletic, military, or event policy applies.
This is why WBGT should not be used as a stand-alone safety decision. It is most useful when paired with activity-specific guidance and a clear action plan.
Practical examples
Sunny field
A soccer field in full sun can have higher heat stress than a shaded area nearby. The air temperature may be the same, but radiant heat from direct sun and the playing surface can increase the heat load on athletes, coaches, officials, and spectators.
Cloudy but humid day
A cloudy day may reduce direct sun, but high humidity can still make cooling difficult. Sweat does not evaporate as efficiently when the air is already holding a lot of moisture. WBGT can remain elevated even when the sun is not intense.
Breezy but exposed location
Wind can help cooling, but it may not offset strong sun, high temperature, heavy exertion, or restrictive clothing. A breezy construction site or open athletic field can still require heat planning when WBGT is elevated.
Shade versus full sun
Moving from full sun to shade can reduce radiant heat exposure, but it does not remove humidity, air temperature, workload, or clothing effects. Shade is an important control, but it is one part of a heat-safety plan.
WBGT thresholds require context
WBGT thresholds can help organizations decide when to add controls, modify activity, increase breaks, adjust equipment, or postpone activity. However, thresholds are not universal safety lines.
A threshold that makes sense for one setting may not be appropriate for another. Outdoor work, football practice, marching band, military training, youth camp, and a public festival may require different actions at the same WBGT.
For a full explanation of how to interpret WBGT action levels, see Understanding WBGT Thresholds.
How to use WBGT responsibly
WBGT is most useful when it leads to earlier, clearer decisions. A responsible approach is to:
- Check conditions early. Look at current and forecast WBGT before the highest-risk period.
- Consider the activity. Workload, exercise intensity, clothing, equipment, and duration matter.
- Account for people. New workers, young athletes, older adults, people returning after time away from heat, and people with health or medication concerns may need more caution.
- Use the right policy. Follow workplace requirements, athletic association rules, school policies, military guidance, event plans, or medical direction that apply.
- Prepare controls. Shade, rest, cooling, hydration access, schedule changes, and trained supervision should be planned before conditions peak.
- Watch for symptoms. Environmental numbers are useful, but symptoms and behavior should always be taken seriously.
WBGT does not replace professional judgment. It gives decision-makers a better view of the heat environment so they can plan more effectively.
How Klimo Insights uses WBGT
Klimo Insights focuses on WBGT because many heat decisions are practical and time-sensitive. People need to know not only that it will be hot, but when heat stress will rise, how conditions may change through the day, and whether there is a better window for activity.
Klimo WBGT tools are designed to support planning for work, sports, events, and outdoor activity. They should be used alongside local knowledge, applicable policies, onsite observations, and trained judgment.
FAQ
What does WBGT stand for?
WBGT stands for Wet Bulb Globe Temperature.
Is WBGT the same as body temperature?
No. WBGT describes environmental heat stress. It does not measure a person’s core temperature or diagnose heat illness.
Why can WBGT be high when the air temperature is not extreme?
Humidity, direct sun, low airflow, and radiant heat from surfaces can all increase heat stress. WBGT accounts for these factors more directly than air temperature alone.
Is WBGT better than heat index?
WBGT is often more useful for outdoor activity planning because it includes sun, radiant heat, and wind. Heat index remains useful for general public weather awareness.
Can I use WBGT to decide whether an activity should stop?
It can help inform that decision, but the answer depends on workload, clothing, acclimatization, policy, available controls, and the people involved.
Source notes
How this page should be used
This explainer is educational. It summarizes how WBGT works and how it is commonly interpreted in heat-safety planning. It is not a substitute for onsite measurement requirements, workplace policies, governing-body rules, or medical judgment.