Wet bulb globe temperature, or WBGT, is one number that combines air temperature, humidity, wind, and sunlight, and published heat policies use that number to tell a coach when to add breaks, remove equipment, shorten practice, or stop. The thresholds differ by region, so a coach needs the table for the right part of the country.
Four news stories from July and August 2026 show why the reading and the record of the reading both matter.
In South Carolina, a jury found a school district grossly negligent after a rising ninth-grader suffered a severe heat stroke at a June 2022 football practice, and awarded $4.8 million. According to the report, the district denied negligence, pointed to its certified athletic trainers, and said it will appeal.
In mid-August, the Associated Press reported about 97 million people under heat advisories as practices began. Two South Carolina districts canceled evening football scrimmages involving more than a dozen high schools.
In Kentucky, two Louisville high school football programs were sanctioned for holding a July scrimmage before finishing the required heat acclimatization protocol. The report describes no injury.
In Kansas, a 17-year-old died on the evening of his team’s first day of practice. KCUR reports the area was about 90 degrees with 58% humidity. The cause of death is undetermined pending autopsy, so the role of heat isn’t confirmed, and this article doesn’t attribute the death to heat or to any failure.
[TL;DR] Highlights and Key Takeaways
- Wet bulb globe temperature measures heat stress in direct sunlight. The heat index is calculated for shade and leaves out sun and wind.
- A handheld WBGT meter, set up in the sun at the practice site, gives the reading that published policies assume. Online tools give an estimate.
- Thresholds differ by region. A published regional table stops outdoor workouts at 92.1°F WBGT in the region with the highest thresholds and at 86.2°F in the region with the lowest.
- Iowa’s and Texas’s policies call for a reading every 30 minutes, taken by the same person where possible.
- A log entry records the date, time, place, reading, device, reader, and the change the coach made.
- A WBGT number isn’t an air temperature. Only 10% of the reading comes from the thermometer.
Quick answers to the questions boards ask
What does our league have to document to survive a heat illness lawsuit?
The answer depends on your state’s law and the facts, so ask an attorney what a court looks for. Four records show what a league did: a written heat policy, a dated roster of coaches trained on the policy, a WBGT reading logged for each practice, and a note of each change made because of a reading. In the South Carolina case, the jury found the district grossly negligent, and the district says it will appeal.
It is 105 degrees at game time. Who decides whether we play, and what happens to our fees if we cancel?
The person named in your written heat policy decides, using a WBGT reading and a published threshold table. If the policy names no one, the board should name a person and a backup before the next game. A 105-degree air temperature or heat index isn’t a WBGT reading, so take one before deciding. What happens to fees depends on your refund policy and on the terms of any event cancellation policy you bought, so ask a licensed agent.
What is heat acclimatization, and what happens if our program skips it?
Heat acclimatization is the gradual increase in practice length, equipment, and intensity over the first two weeks of a warm-weather season. The 14-day schedule is covered in a separate article. For a school program, skipping the schedule can bring sanctions: in Kentucky, the school district and the state association canceled scrimmages and full-gear practices, fined each school $250, and put two programs on probation. A community league may answer to no state rule, so check with your sports organization.
What is our league required to do for heat at the first practice of the season?
The answer depends on your state and on whether the program is a school team or a community league. Texas requires school programs to take a WBGT reading before every outdoor practice and says readings should continue during practice, while many community leagues answer only to their own sports organization’s rules. A sound minimum for the first practice is a dated acclimatization schedule, a WBGT reading with a threshold table, an emergency action plan, and a log.
What wet bulb globe temperature measures
The National Weather Service defines WBGT as a measure of heat stress in direct sunlight that takes into account temperature, humidity, wind speed, sun angle, and cloud cover.
The Korey Stringer Institute at the University of Connecticut publishes the formula. Seventy percent of the number comes from the wet bulb temperature, which reflects humidity. Twenty percent comes from the globe temperature, which reflects radiant heat from the sun. Ten percent comes from the ordinary air temperature.
A WBGT reading isn’t an air temperature. A coach who compares a WBGT reading of 85°F to a forecast high of 85°F is comparing two different things.
Did you know? Only 10% of a WBGT reading comes from the air temperature, according to the formula the Korey Stringer Institute publishes. Humidity accounts for 70%.
How WBGT differs from the heat index
The heat index uses temperature and humidity only, and the National Weather Service says the heat index is calculated for shaded conditions. WBGT is measured in direct sunlight and adds wind, sun angle, and cloud cover.
The National Federation of State High School Associations (NFHS) adds that the heat index assumes a standard-sized adult walking at 3.1 miles per hour in the shade. A child running drills on a sunny field doesn’t match those assumptions. The NFHS calls WBGT “the gold standard” for measuring heat stress during hot weather.
How to get a WBGT reading
A coach has two options: a handheld meter at the field, or an estimate from an online tool.
A handheld meter
A handheld WBGT meter measures conditions where the players are. The Korey Stringer Institute names the Kestrel 5400 and the QuestTemp as examples of devices on the market. Prices vary by model and change over time, so get current quotes.
The NFHS and the Iowa high school associations’ WBGT guidance describe the same setup steps:
- Set up the meter at the practice site 15 to 20 minutes before activity starts, so the sensors adjust.
- Place the meter at least three feet off the ground and away from obstructions.
- Place the meter in the sun, not in the shade. If the team practices on turf, place the meter on the turf.
- Take the first reading before practice starts.
- Take a new reading every 30 minutes and adjust practice if the reading moves into a different band.
- Practice with the device before the first hot day.
Online tools and estimates
Where a league has no meter, an online tool gives an estimate. The National Weather Service’s Tulsa office offers a WBGT calculator that uses location, temperature, dew point, wind speed, and cloud cover. The page labels the calculator a prototype that isn’t for operational use.
The Korey Stringer Institute also describes estimation charts built from temperature and humidity alone. According to the institute, those charts assume full sunshine and light wind.
An estimate describes a weather station or a forecast grid, not your field. Iowa’s guidance says weather apps and local forecasts don’t give an accurate reading for the spot where the activity takes place. Texas’s rule accepts either method: schools must use a scientifically approved WBGT instrument or another scientifically proven method, such as internet-based weather station software. If you use an estimate, write “estimate” and the tool’s name in the log.
Wet bulb globe temperature thresholds by region
No single WBGT threshold applies across the country. The published regional table sets different numbers for each of three regions.
The following table comes from a Korey Stringer Institute handout of regional guidelines. The handout adopts the table from Grundstein and colleagues’ 2015 study in the journal Applied Geography, which based the activity guidelines on Georgia High School Association policy. Category 3 has the highest thresholds and Category 1 has the lowest. The values are WBGT readings in °F, shown as published.
| Category 3 | Category 2 | Category 1 | Activity guideline |
|---|---|---|---|
| Below 82.0 | Below 79.7 | Below 76.1 | Normal activities. At least three rest breaks each hour, at least 3 minutes each. |
| 82.2 to 86.9 | 79.9 to 84.6 | 76.3 to 81.0 | Use discretion for intense or prolonged exercise. At least three rest breaks each hour, at least 4 minutes each. |
| 87.1 to 90.0 | 84.7 to 87.6 | 81.1 to 84.0 | Maximum practice time is 2 hours. Football players are restricted to helmet, shoulder pads, and shorts. All sports: at least four rest breaks each hour, at least 4 minutes each. |
| 90.1 to 91.9 | 87.8 to 89.6 | 84.2 to 86.0 | Maximum practice time is 1 hour. Football: no protective equipment and no conditioning. All sports: 20 minutes of rest breaks spread through the hour. |
| 92.1 and above | 89.8 and above | 86.2 and above | No outdoor workouts. Delay practice until a cooler WBGT is reached. |
The gap between regions is large. A reading of 86.5°F WBGT falls in the “no outdoor workouts” band for Category 1 and in the “use discretion” band for Category 3.
How to find your region and your own table
The NFHS article includes a map of the three categories. State associations then write their own tables from the regional numbers. Iowa’s associations state that Iowa is in Category 2, and Iowa’s table stops outdoor activities above 89.7°F WBGT.
Texas is split between two regions. The University Interscholastic League’s 2026-2027 heat plan sets a threshold of 79.7°F for Class 2 regions and 82°F for Class 3 regions. At or above that number, rapid cooling zones become mandatory.
A state table can also differ from the regional table in its details. Iowa’s guidance adds a separate, stricter table for middle school activities. If a state association or your sports organization publishes a table, use that table. If neither does, the regional table in this article is a published starting point, and your league’s medical advisor or a local athletic trainer can help the board adopt one.
Did you know? Iowa’s WBGT guidance publishes a separate table for middle school activities. At the second band, that table calls for four rest breaks an hour where the high school table calls for three.
Who reads the meter and who writes it down
Iowa’s guidance says the same person should monitor WBGT throughout the event. Texas’s plan recommends the same, where possible. One reader means one method, one spot on the field, and one set of handwriting in the log.
Iowa’s guidance says on-site medical personnel should take the readings if available, or otherwise the administrator overseeing the event, and that the reader tells the coaching staff about changes before and during practice. Many community leagues have no athletic trainer. A league in that position can name a reader for each team, such as an assistant coach or a team parent, plus a backup.
The written heat policy should answer three questions by name or by role:
- Who takes the reading and keeps the log?
- Who decides to change, shorten, or stop practice when the reading crosses a band?
- Who takes over each job when that person is absent?
What a WBGT log entry contains
Texas’s plan recommends that schools record WBGT readings for outside practices and keep them on file. Neither the Texas plan nor the Iowa guidance prescribes a log format, so the following list is a suggested format built from what those policies ask a reader to do.
Each reading gets one line:
- Date and time of the reading.
- Location: the field, and the surface if the site has both grass and turf.
- WBGT reading.
- Method: the meter’s model, or the name of the online tool and the word “estimate”.
- Reader’s name.
- Band and table: which band the reading falls in, and which table the league uses.
- Action taken: the change the coach made, such as added breaks, removed equipment, a shortened practice, or a canceled practice. If the reading required no change, write “none”.
- Practice start and end times. Iowa’s guidance counts the start as the moment the first athlete steps on the field.
A paper notebook in the equipment bag works, and so does a shared spreadsheet. Write each entry at the time of the reading, not from memory afterward.
Decide who keeps the logs after the season and for how long. How long to keep records is a legal question, so ask an attorney.
What to do when the reading crosses a band
If the reading moves into a higher band during practice, follow the higher band from that point. Iowa’s guidance says the reading at the start of practice sets the lowest category to follow, and a higher reading moves practice into the higher category.
If the reading reaches the top band, outdoor practice stops until a lower reading is recorded.
A WBGT table doesn’t replace the rest of a heat plan. Players still need unrestricted access to water, the first two weeks still follow the acclimatization schedule, and the emergency action plan still covers cooling and 911. A separate article covers the signs of heatstroke and dehydration.
Frequently Asked Questions
What is a dangerous wet bulb globe temperature for youth sports?
The answer depends on the region. The regional table published by the Korey Stringer Institute stops outdoor workouts at 86.2°F WBGT and above in Category 1, 89.8°F and above in Category 2, and 92.1°F and above in Category 3. Practice changes begin at lower readings. If your state association or sports organization publishes a table, follow that table.
Is WBGT the same as the heat index?
No. The heat index uses temperature and humidity and is calculated for shade. WBGT is measured in direct sunlight and adds wind, sun angle, and cloud cover, according to the National Weather Service.
Can a coach use a phone weather app instead of a meter?
An ordinary weather app reports air temperature or heat index, not WBGT. Iowa’s guidance says apps and local forecasts don’t give an accurate reading for the practice site. An online WBGT tool gives an estimate, and the log should label the number as an estimate.
How often should a coach take a reading?
Texas requires school programs to take a reading within 15 minutes before practice, and its plan says readings should be taken every 30 minutes during practice. Iowa’s guidance also says every 30 minutes.
Does WBGT matter for indoor practice?
WBGT can matter indoors. Iowa’s guidance applies to gyms without climate control and says to switch the meter to indoor mode in those buildings.
Do we still need heat acclimatization if we use WBGT?
Yes. Iowa’s guidance says acclimatization still has to take place at the start of the season. WBGT governs each day’s practice, and acclimatization governs the first two weeks.
Are the thresholds lower for younger children?
Some tables are stricter for younger athletes. Iowa’s middle school table requires more rest breaks at the second band than its high school table does. Ask your sports organization or a medical advisor which table fits your age groups.
Glossary of Terms
- Wet bulb globe temperature (WBGT): a measure of heat stress in direct sunlight that combines temperature, humidity, wind speed, sun angle, and cloud cover.
- Heat index: a measure that combines air temperature and humidity, calculated for shaded conditions.
- Wet bulb temperature: the part of a WBGT reading that reflects humidity. The wet bulb temperature makes up 70% of the number.
- Globe temperature: the part of a WBGT reading that reflects radiant heat from the sun. The globe temperature makes up 20% of the number.
- Category 1, 2, and 3: the three heat safety regions in the Grundstein study. Category 3 has the highest thresholds.
- Activity band: a range of WBGT readings tied to one set of practice rules. Many tables color the bands green, yellow, orange, red, and black.
- Work-to-rest ratio: the balance of activity time and break time in each hour of practice.
- Korey Stringer Institute: a research and advocacy institute at the University of Connecticut that publishes heat safety guidance for athletes.
- NFHS: the National Federation of State High School Associations, which writes rules and guidance that state associations can adopt.
- Heat acclimatization: the gradual increase in practice length, equipment, and intensity over the first two weeks of a warm-weather season.
What a WBGT log means for a league’s insurance
Some insurance applications ask about a league’s safety policies, and a written heat policy with a dated WBGT log is a useful record to have. These records don’t affect what any policy covers, so ask a licensed agent about your own policy.
For the full written plan, including cooling, hydration, and coach training, see Sadler Sports Insurance’s guide to heat illness prevention in youth sports.