Simple Outdoor WBGT Calculator
Quickly calculate WBGT with our simplified WBGT calculator, and then see how Perry Weather’s on-site WBGT monitoring system calculates WBGT the right way, so you can stop guessing and start protecting.
What is Wet Bulb Globe Temperature (WBGT)?
If you’re making heat safety decisions for student-athletes, workers, or outdoor events, you’ve likely come across the term WBGT—short for Wet Bulb Globe Temperature. But what exactly does it mean and how is WBGT calculated?
Wet Bulb Globe Temperature, or WBGT, is your body’s true heat stress scorecard.
Wet bulb globe temperature (WBGT) is a measure of how direct sunlight truly feels to the human body, factoring in multiple environmental elements to gauge heat stress.
Unlike the heat index, which only considers temperature and humidity, calculating WBGT factors in the sun’s intensity, wind, and cloud cover. Here’s a quick video explaining the differences.
Calculating WBGT isn’t just for the weather geeks—it’s essential for anyone who spends time outdoors in the heat.
What is the WBGT Index, Anyway?
The WBGT index is the gold standard for measuring the impact of heat stress on the human body in real-world conditions.
It’s the official metric used by everyone from the NCAA and state high school athletic associations to OSHA and the U.S. Military to make critical safety decisions.
WBGT readings, unlike regular temperature readings, combine the effects of:
- Air temperature and air movement
- Relative humidity
- Radiant heat or Sun angle
- Cloud cover (solar radiation)
According to the National Weather Service, WBGT is a better metric if you work or exercise in direct sunlight. It’s the gold standard for measuring heat stress in outdoor and athletic environments.
WBGT is a composite value made up of:
- Dry bulb temperature (Tdb) – your standard air temperature
- Natural wet bulb temperature (Tnwb) – measures evaporative cooling (humidity + airflow)
- Globe temperature (Tg) – measures radiant heat from the sun and surroundings
To effectively manage heat exposure, it’s crucial to grasp the components and methods behind calculating WBGT. This understanding is essential whether you use a dedicated WBGT calculator, convert from dry bulb to wet bulb temperature, or perform the WBGT calculations by hand.
How WBGT is Calculated: The Wrong Way vs. The Right Way
If you’ve ever Googled “how to calculate WBGT,” you’ve likely found a simple formula that seems easy enough. But that common online calculator (like the one above) is a theoretical shortcut—and it’s dangerously incomplete.
The Common Shortcut: The “Stull Method” Estimation
Many free apps and online tools use an estimation known as the Stull Method. It’s a formula designed to guess one component of the reading—the Wet Bulb Temperature (Tw)—using only two basic data points: air temperature and relative humidity.
Tw ≈ T × atan(0.151977 × RH+8.313659
)) + atan(T + RH) – atan(RH – 1.676331) + 0.00391838 × RH$^{3/2}$ × atan(0.023101 × RH) – 4.686035
Where:
- T = dry bulb air temperature in Celsius (°C)
- RH = relative humidity in percent (%)
The problem? It completely ignores the two biggest factors that determine real-world heat stress on an athlete:
- Solar Radiation (the sun beating down)
- Wind Speed (a cooling breeze)
The Stull Method was designed as a simple alternative when a professional WBGT monitor isn’t available. This gives a modeled approximation of wet bulb temp, which can be plugged into a simplified WBGT formula.
Relying on it is like predicting a game’s final score by only looking at one team’s stats. You’re missing half the story, which is why this method doesn’t meet the safety standards for organizations like the NCAA or OSHA.
Real Natural Wet Bulb Calculation (What Perry Weather Now Uses)
Perry Weather now uses a more accurate method — often called the Natural Wet Bulb Calculation combined with real on‑site sensors — to generate WBGT. This method mirrors what full WBGT meters do.
Professionals rely on direct measurement using the official WBGT formula. Instead of estimating, Perry Weather’s on-site hardware directly measures all the critical variables in real-time.
Here’s what’s different & how it works, in simple terms:
- Sensors on site measure more environmental inputs:
- – Air temperature (dry bulb)
- – Relative humidity
- – Wind speed
- – Solar radiation or direct sunlight (often via globe or black bulb)
- – Atmospheric pressure or similar metadata (to fine‑tune wet bulb)
- The natural wet bulb temperature (T<sub>nwb</sub>) is calculated with those inputs (not just temp + humidity) so the value reflects what’s really happening outside — not a shaded theoretical spot.
- Then WBGT is computed using the same weighted formula:
WBGT = 0.7 × T<sub>nwb</sub> + 0.2 × T<sub>g</sub> + 0.1 × T<sub>d</sub> - Because it updates often (every few minutes) and uses actual environmental data, this gives athletic trainers more accurate, actionable readings.
It looks like this:
WBGT = (0.7 * Tw) + (0.2 * Tg) + (0.1 * T)
In this WBGT formula, there are three important variables to note:
- T = Temperature in Celsius
- Tg = Globe Thermometer Temperature (in Celsius) – this is measured by a thermometer placed in a special black globe to estimate solar radiation without the effects of the light itself
- Tw = Wet-bulb Temperature (in Celsius)
But you don’t need to memorize this. Perry Weather takes care of wet bulb temperature calculation for you! Unlike theoretical models, Perry Weather’s WBGT calculation is automated, continuous (every 5 minutes), and based on your location—not a weather station 5 miles away.
Why do I need to monitor WBGT?
Wet bulb globe temperature helps in maintaining a proper workload in direct sunlight as well as deterring heat strokes during an excessive heat warning.
This is especially important as it differs from the heat index, which only accounts for temperature and humidity in its calculation for shaded areas.
WBGT thermometers have been growing in popularity and usefulness, especially for youth sports and athletic programs.
States like Georgia have begun mandating the use and monitoring of WBGT for all high school outdoor athletic programs. The University Interscholastic League (UIL) has recommended Texas athletic programs to start using WBGT and moving away from heat index.
When schools and organizations follow wet bulb weather and its guidelines, they can make better decisions about:
- when it’s safe to be outside practicing
- hydration and how often to take water breaks
- whether to use pads during practices
- if they should cancel practice and physical activity
- if they should move practice or the event indoors
Read more about monitoring WBGT here.
Why Use WBGT to Calculate Heat Stress?
- It’s Apt for Outdoor Activity: Since WBGT is a measure of heat-related stress specifically, it is an important factor to consider anytime people are performing some kind of outdoor activity, like construction activities and for calculating work/rest schedules.
To ensure the safety of working conditions, regulations are in place for WBGT monitoring, making it essential to calculate WBGT accurately.
- WBGT is Highly Valuable for High School and Collegiate Athletics: WBGT is also highly valuable information for high school and collegiate athletics, event venues, OSHA regulated construction, city sports leagues, and military training facilities. The applications are endless.
For example, during a high school football practice, kids are training their hearts out in the heat of August. Knowing the wet bulb globe temperature can ensure that players in direct sunlight will not put a dangerous amount of stress on their bodies, as well as help the coaches know how often they can take breaks and need hydration.
- WBGT can even show you when humidity decreases: A humidity decrease generally causes a rise in temperature, which is perfect for snowmakers. Therefore, being able to calculate WBGT is also beneficial for winter sports and activities.
What is Wet Bulb Temperature?
When water evaporates into the air it creates a cooling effect, but the amount of this cooling varies depending on the overall air temperature and the relative humidity.
Wet-bulb temperature measures how cool the air can become through water evaporation. It’s influenced by both temperature and humidity. Essentially, it reflects the body’s ability to cool itself through sweating.
Here is the equation for wet bulb temperature:
This is a rather complex WBGT formula:
Tw = T * arctan[0.151977 * (rh% + 8.313659)^(1/2)] + arctan(T + rh%) – arctan(rh% – 1.676331) + 0.00391838 *(rh%)^(3/2) * arctan(0.023101 * rh%) – 4.686035
Here, “T” is the temperature in celsius, and “rh” represents the relative humidity.
With this final calculation, you can calculate WBGT completely.
Learn more about the differences between wet bulb temperature and wet bulb globe temperature here.
Best Ways to Calculate WBGT
Whether you’re an athletic trainer or organizing an outdoor event, knowing how to calculate wet bulb globe temperature can be a game-changer for heat safety.
A single missed WBGT reading can delay action. A single wrong reading can lead to heat illness—or worse. And the truth is, not all WBGT methods are created equal.
Knowing the right formula is one thing. Applying it consistently is another. The best way to calculate WBGT is with an automated, on-site system that removes the risk of human error and inefficiency.
Option 1: Calculate WBGT by Hand
(.07 * Wet-bulb Temp) + (0.2 * Globe Thermometer Temp) + (0.1 * Temperature) = Wet Bulb Globe Temperature
This is the official equation recommended by OSHA, ISO, and NWS—but only if you have the right sensors.
To calculate WBGT manually:
- You need a black globe thermometer (to measure radiant heat)
- A psychrometer or sling thermometer (for wet bulb temp)
- A dry bulb thermometer (for air temp)
- And the time and training to record readings every 15 to 30 minutes.
Bottom line: This method is scientifically sound but totally unscalable for athletic trainers, coaches, or field personnel managing real-time safety.
Option 2: Weather Apps
Relying on a generic weather app for WBGT is like trying to tape an ankle with duct tape. It might feel like you’re doing something, but you’re not using the right tool for the job, and it’s going to fail you when it matters most.
Many of these apps use the Stull method, a mathematical estimate of wet bulb temperature based solely on air temperature and humidity. They don’t measure solar radiation or wind, and they often pull data from the nearest National Weather Service station, which could be 5–25 miles away.
Pros:
– Convenient and easy to use
Cons:
– Only hourly updates. A lot can change in an hour
– No site-specific data. Pulls data from the National Weather Service, which could be up to 25 miles away.
– Often shows inaccurate measurements.
Option 3: Handheld WBGT Devices
These portable handheld WBGT monitors are built for field use, and they do measure key components of WBGT. But most have serious limitations that compromise accuracy and usability—especially when you’re busy managing athletes.
Pros:
– Portable
– Durable; Built for outdoors
Cons:
– Too manual: Lacks automated WBGT data logging features
– Inaccurate readings: Small black bulb sensor causes massive spikes in WBGT readings
– Lacks radiation shield, leading to erroneously high WBGT readings
Okay, that was a lot. But don’t panic!
You don’t really need a WBGT calculator or a formula to calculate the WBGT accurately. There are much faster and much, much easier ways to calculate wet bulb globe temperature.
Option 4: Perry Weather
For regular users of wet bulb globe temperature calculations and regulations, it’s best to use an integrated WBGT calculator service or a WBGT device for up-to-date information. Perry Weather offers weather monitoring software and hardware to simplify the entire WBGT monitoring process and eliminate the manual guesswork altogether.
Perry Weather uses an on-site sensor system that automatically logs WBGT readings every 5 minutes, with policy-based alerts triggered instantly when thresholds are crossed.
No manual checks. No interpretation. No missed readings.
Perry Weather is designed for people like you who can’t afford to “guess” when it comes to heat risk. We combine:
- On‑site black bulb sensors for accurate radiant heat measurements
- Natural wet bulb calculations that account for wind, solar radiation, and humidity—not just lean approximations
- Automated, continuous logging so you have records for every practice, every event
- Custom alerts tied to your specific heat policy thresholds (UIl, CIF, TSSAA, etc.)
- Visibility across your team so coaches, trainers, safety officers all see the same numbers
Learn more about how Perry Weather tracks the wet bulb globe temperature and how it can help you here
Watch how our customers use Perry Weather to calculate WBGT
Watch more customer stories here
How Do I Calculate the Wet Bulb Globe Temperature (WBGT)?
The wet bulb globe temperature (WBGT) can be measured with on-site weather stations, handheld devices known as WBGT monitors, or online WBGT and weather monitoring apps.
These tools calculate the temperature, humidity, and sunlight to compute the WBGT index.
How can I take a WBGT reading?
Wet bulb globe temperature readings can be taken using a WBGT monitoring device like a weather monitoring station or a handheld monitor. Readings must be taken by an athletic director/administrator or medical personnel overseeing the event.
The WBGT should be monitored throughout the event and readings must be taken every 20 to 30 minutes, with athletic activities being adjusted accordingly.
Participation modifications must be communicated to the coaching staff before and during practice.
Why Should I Track the WBGT?
Regularly monitoring the WBGT levels allows coaches and athletic trainers to adjust training schedules, implement hydration protocols, and make informed decisions to protect athletes from high temperature and heat-related risks.
Tracking the WBGT is crucial to protect athletes’ health and safety during outdoor practices, games, and events.
How often should we track WBGT?
WBGT should be measured regularly, especially during periods of high heat or physical activity. The frequency depends on the specific situation and guidelines.
Can I calculate WBGT using a smartphone app?
While some apps provide estimates of WBGT, WBGT monitors and weather stations like Perry Weather offer more accurate and reliable measurements.
Are heat index and wet bulb globe temperature the same?
No. WBGT is best used outside any building, athletic center, or any area that is climate controlled. Heat index, on the other hand, is best used within any building, athletic center, and casual, shaded environments. Learn more here.
So, What’s the Best Way to Calculate WBGT?
If you’re responsible for heat safety, you need more than a formula—you need proof, precision, and a process that scales.
With Perry Weather, you don’t just get a number. You get:
- Reliable data updated every 5 minutes
- Automatic alerts based on your school’s exact heat policy
- Built-in compliance protection with downloadable audit logs
- A single source of truth for every coach, trainer, and director on staff
It’s not just smarter—it’s safer.
Sign up for a free trial and see Perry Weather in action for yourself!
