National Weather Service United States Department of Commerce

Wet Bulb Globe Temperature

(Experimental. Not for operational use)


Maximum Wet Bulb Globe Temperature

day 1 wbgt
Day 1
day 2 wbgt
Day 2
day 3 wbgt
Day 3
day 4 wbgt
Day 4
day 5 wbgt
Day 5

What is WBGT?

Wet Bulb Globe Temperature (WBGT) is a measure of heat stress in direct sunlight, which takes into account: temperature, humidity, wind speed, sun angle and cloud cover (solar radiation). This differs from the more commonly known heat index, which takes into consideration temperature and humidity and is calculated for shady areas.

WBGT can be used to establish guidelines for activity modifications during physical activity in the heat. Guidelines will vary geographically since temperatures fluctuate by region, and people's response to heat will also vary by the region they are acclimated to. Outdoor workers, people doing strenuous outdoor activities, and athletes or marching bands are a few examples of people who can benefit from the use of WBGT.

Bottom-line upfront >>>> what value should you use? For day-to-day activities, heat index will serve you well. If you work outside or plan on any sort of vigorous outdoor activity in the full sun, use the WBGT.  


Comparing WBGT and Heat Index
Heat Index
Measured in the sun
Measured in the shade
Uses Temperature
Uses RH
Uses Wind
Uses Cloud Cover
Uses Sun Angle
Temp F Dew Point F RH % Sky % Wind mph Heat Index F WBGT F
90 65 42 05 03 92 89
90 65 42 05 13 92 83
90 65 42 65 13 92 81
90 70 52 10 06 96 88
90 70 52 60 06 96 86
90 70 52 60 13 96 85
100 70 39 10 13 108 90
100 70 39 10 5 108 94
100 70 39 65 05 108 91


Wet Bulb Globe Temperature

Initial values are estimates
for the selected location
adjust sliders as needed
Fcst Max Temp(F):
Wind Speed(mph):
Cloud Cover(%):


Map, calculator courtesy National Weather Service - Tulsa

Guidelines - Charts

While there is not set criterion for WBGT temperatures and related risks/impacts, the American College of Sports Medicine (ACSM) has developed a set of values that have been accepted as a standard to follow. Their original guidelines were developed for running events, but have since been expanded to include intermittent (non-continuous) activities [Medicine & Science in Sports & Exercise: March 2007 - Volume 39 - Issue 3 - p 556-572] . The guidelines are not based on location.

Using ACSM as a starting point, further research by the University of Georgia (UGA) factored in climatology and regional differences in an effort to incorporate acclimatization* into the guidelines. 

The military and OSHA also have devised recommendations, as do many university and high school athletic departments.

It should be noted that while WBGT will provide solid guidelines, other factors such as an individual’s physical fitness, acclimatization, medical condition, and age also have an impact.

* Acclimatization: the body's natural adaptation to heat/cold. The process usually takes 10 to 14 days.



NOT based on location - American College of Sports Medicine

Continuous Activities   Intermittent Activities

Activities with little if any break, such as cross country running, 5K runs, and marathons.

Activities that generally have breaks between bursts of high intensity movements/actions, such as football, soccer, lacrosse, etc.

ACSM wbgt guidelines for continuous activities ACSM wbgt guidelines for training or non-continuous activities

Guidelines from the American College of Sports Medicine - not based on location

Guidelines from the American College of Sports Medicine - not based on location


Based On Location

The following recommendations use similar criteria as the ACSM, but modified for location and climatology. This adjustment factors in the acclimatization that occurs for those that consistently work and exercise in hot environments.
UGA guidelines regional categories

Guidelines from the University of Georgia

Regional Categories



Heat Safety and Additional Resources



  • Reschedule or postpone outdoor plans during peak heating of the day (usually mid to late afternoon)
  • Check in with family members, friends. Make sure they have a way to keep cool and take necessary precautions from the heat. The elderly and children are especially susceptible to the heat. 
  • Don't forget your pets! Make sure they have adequate shelter (preferably indoors, air conditioned) and ample water. 


  • Take frequent breaks in the shade or in an air conditioned location. Strenuous outdoor activities should be reduced (or eliminated), especially in direct sunlight where there is little ventilation.
  • Drink plenty of water or other non-alcohol fluids. Stay hydrated by drinking plenty of fluids even if you do not feel thirsty. Avoid drinks with caffeine or alcohol.
  • Continue to check on family, friends and your pets. 
  • Don’t get too much sun. Sunburn makes the job of heat dissipation that much more difficult