Work out WBGT from weather data, or exactly from three thermometer readings.
What is wet bulb globe temperature?
Wet bulb globe temperature, or WBGT, is a single number that describes how hard the heat is actually working on a body outdoors.
Air temperature only tells part of the story. A 90 degree afternoon in dry shade with a steady breeze is a very different thing from 90 degrees in still, humid air under full sun. WBGT folds four factors into one reading: air temperature, humidity, wind speed, and solar radiation. That is why it is the measurement written into heat guidelines for athletics, the military, and occupational safety, rather than the temperature on a car dashboard.
This app puts that reading in your pocket, for your location or any city you search.
Difference between heat index and WBGT
People often reach for the heat index, but the two measurements answer different questions.
| Factor | Heat index | WBGT |
|---|---|---|
| Inputs | Air temperature and relative humidity | Air temperature, humidity, wind speed, and solar radiation |
| Assumed conditions | Shade, light wind | Direct sun, measured wind |
| Typical use | General public heat warnings | Athletic, military, and occupational safety guidelines |
| Reported as | An apparent or feels like temperature | A heat stress index with flag categories |
In short, if people are working or training in the sun, WBGT is the number that matches the situation.
WBGT flag conditions
A raw number is only useful if it tells you what to do. The app translates each reading into color-coded flag levels, white, green, yellow, red, and black, following the U.S. military heat category system that athletics and outdoor industries have adopted widely.
Thresholds and recommended actions differ depending on who you are and what you are doing, so the app carries five guidance modes: Athlete, Military, Outdoors, Aviation, and OSHA. Pick the one that matches your situation and the guidance adjusts with it, along with a built-in reference chart for flag categories and activity recommendations.
Who uses a WBGT tool
Athletic trainers and coaches
Set practice modifications, break schedules, and equipment decisions against published heat guidelines instead of judgment calls.
Military and first responders
Flag conditions have guided training and work limits for decades. Check the category before a formation steps off.
Industrial safety and outdoor crews
Construction, roofing, landscaping, and utility work. Plan work and rest cycles and know when to shift to early hours.
Aviation and ground operations
Ramp and flight line crews working long stretches on open pavement in full sun.
What the app shows
- Real-time WBGT for your current location or any city you search.
- Color-coded flag level with guidance for your selected mode.
- Hourly and 14-day WBGT forecasts, so you can plan a practice or a shift ahead of time.
- The underlying conditions: humidity, wind, solar radiation, cloud cover, and pressure.
- Fahrenheit or Celsius.
How the calculation works
A proper WBGT reading traditionally requires a physical instrument: a wet bulb thermometer, a black globe thermometer, and a dry bulb thermometer, read together on site. Most people do not have that kit standing on a sideline.
Instead, the app estimates WBGT from standard meteorological inputs using the Liljegren et al. (2008) model, a peer-reviewed method developed at Argonne National Laboratory that solves the physical heat balance of the black globe and wet bulb rather than relying on a rough approximation. Weather data comes from Open-Meteo.
The practical result: a reading grounded in the same physics as the instrument, available anywhere your phone has a signal.
Common questions
What does WBGT stand for?
Wet bulb globe temperature. The name comes from the instruments used to measure it: a wet bulb thermometer for humidity and evaporation, and a black globe thermometer for radiant heat from the sun.
Is wet bulb globe temperature the same as wet bulb temperature?
No, and the distinction matters. Wet bulb temperature alone measures evaporative cooling. WBGT is a weighted composite that includes wet bulb temperature along with the black globe reading and dry air temperature, which is why it reflects outdoor heat strain more completely.
What is a dangerous WBGT reading?
There is no single universal cutoff. Thresholds depend on the guideline you follow, whether people are acclimatized, and what equipment they are wearing, which is why the app offers separate Athlete, Military, Outdoors, Aviation, and OSHA modes rather than one generic scale. Follow the standard that governs your activity, such as your state athletic association or your employer's heat illness prevention plan. In Texas, for example, the UIL now requires WBGT for outdoor practices and marching band; see the UIL WBGT rules and levels for 2026.
Is the app free?
The app is free to download. An optional Pro upgrade is available as a monthly, annual, or lifetime in-app purchase.
Does it work outside the United States?
Yes. You can search any city, and readings display in Fahrenheit or Celsius.
WBGT guides by setting
Thresholds, who takes the reading, and what has to change, written for each setting the number is used in.
The full level chart in Fahrenheit and Celsius with activity guidance.
Practice modification, football and pads, and what athletic trainers monitor.
ACGIH limits, work-rest cycles and building a heat illness prevention plan.
Categories 1 to 5, work-rest cycles, water intake and clothing adjustments.
One campus policy for athletics, marching band, PE, recess and preschool.
GHSA, FHSAA, UIL and more: where the state thresholds actually diverge.
Get the real heat number
Free to download on iPhone.
