When it comes to protecting student-athletes and staff from heat stress, the heat index just doesn’t cut it. Sure, it tells you how hot it feels like, but does it factor in the blazing sun on the turf? Or the hours your athletes spend pushing through practice? Nope. Enter Wet Bulb Globe Temperature (WBGT)—the game-changing weather safety metric.

This blog breaks down the key differences between the heat index and WBGT, why relying on the old standard can put your teams at risk of extreme heat stress, and how you can start using WBGT today with Perry Weather to keep your athletes safe.

What Is the Heat Index? The “Feels Like” Temperature

Ever stepped outside, checked the weather app, and thought, “It says 90°F, but it feels like a sauna out here?” That disconnect comes from the heat index, also known as the “feels like” temperature.

The heat index estimates how hot your body feels based on air temperature and relative humidity. Think of it as the weather’s way of saying, “The thermometer might read 90°F, but with this sticky humidity, your body is experiencing something closer to 105°F.” Use the heat index calculator below to check the heat index in your area.

The heat index tells you how sweat—your body’s natural cooling system—responds to the environment. On dry days, sweat evaporates quickly, keeping you cool. But when humidity increases, the air gets saturated with moisture, slowing sweat evaporation, making you feel hotter.

Heat Index Calculator

Our simple heat index calculator helps you automatically measure the heat index and what the temperature outside “feels like” quickly and efficiently without any complicated input.

Limitations of the Heat Index

While the heat index might explain why your body feels uncomfortable, when it comes to keeping people safe in extreme heat, it’s only part of the story. Some of the key limitations of the heat index include:

• The heat index ignores direct sunlight, wind, and heat-absorbing surfaces like turf or tracks.
• The heat index fails to represent real-world risks for outdoor activities.

That’s why you need a more comprehensive approach. That’s where WBGT comes in!

What is Wet Bulb Globe Temperature (WBGT)?

Wet Bulb Globe Temperature (WBGT) in a nutshell is an in-depth measurement that takes into account more of the environment (Direct sunlight, water vapor capacity, cloud coverage, etc.). That’s why wet bulb globe temperature (WBGT) is the best metric to calculate heat stress on the human body.

Learn more about wet bulb globe temperature here.

A Clearer Picture: Differences between WBGT and Heat Index

Let us find some common ground real quick. Both Wet Bulb Globe Temperature (WBGT) and Heat Index take into account temperature and relative humidity and aim to fulfill the same purpose. They measure the human body’s ability to resist heat stress. Additionally, they share some similar variables as well, essentially both taking into account ambient temperature and humidity. However, that’s where the similarities end.

When it comes to measuring heat, not all conditions are created equal. The heat index only accounts for shady areas, giving a false sense of comfort, while the wet-bulb globe temperature (WBGT) is designed for areas exposed to the sun, offering a more accurate reflection of how the body actually experiences heat. The heat index ignores the brutal realities of direct sunlight, hot surfaces, and even physical exertion. Here’s why that’s a problem:

Scenario 1: The Heat Index Misleads
On a humid, sunny afternoon, the heat index might say it’s 95°F. That doesn’t account for athletes running drills under the beating sun, which pushes their bodies well past the comfort zone. WBGT, on the other hand, would reveal a much higher and more dangerous heat level, urging immediate safety measures.

Scenario 2: WBGT in Effect
Imagine you’re a high school football coach and your team is practicing on a synthetic turf field. The air temperature is 90°F, but the turf absorbs and radiates heat, while the sun adds extra intensity. WBGT considers these factors, showing the real danger that the heat index overlooks.

Here are some side by side examples of WBGT and Heat Index:

When to Use WBGT vs. Heat Index for Heat Stress Assessment

For anyone responsible for safety in high-risk conditions, WBGT isn’t just a tool—it’s a necessity. WBGT far outperforms Heat index in accuracy, but where do we use it? The great outdoors! WBGT is used best outside any building, athletic center, or any area that is climate controlled. Simple as that, any area outside in direct sunlight is where this index shines bright, so to say.

Heat index, on the other hand, is best used within any building, athletic center, and casual, shaded environments. This could be an old gym without A/C, large covered athletic complex, construction site that does not have proper ventilation/air movement through it, anything that does not involve direct sunlight. It factors in temperature and humidity but assumes you’re not in direct sunlight or doing anything strenuous.

If you’re overseeing student-athletes practicing on turf, or workers on an exposed construction site, WBGT is the gold standard. For those managing student-athletes, WBGT offers actionable insights to schedule practices safely, enforce hydration breaks, and know when to move activities indoors. The heat index can’t do that—it’s more like a vague guess, while WBGT delivers the truth you need to make informed decisions.

WBGT for better heat stress management and safety

To be blunt, having a more accurate metric for heat stress allows for better preparedness in extreme environmental conditions. Think of it this way: the heat index is like a car’s temperature gauge—it gives you some information, but skips the details that could lead to serious trouble. WBGT, on the other hand, is the full diagnostic report.

If you are responsible for the safety of hundreds, if not thousands of people, are you going to want something that’s “close enough” or do you want the best and most accurate product in the field?

There are plenty of government agencies that use this index, in addition to plenty of organizations and Academic/Athletic institutions. This includes the U.S. Military, the American Conference of Governmental Industrial Hygienists, American College of Sports Medicine, National Weather Service, OSHA, and countless Universities. Although this tool has been well established for years, many people are still just now finding out about it. Every day, more and more people are catching up to the standards of environmental weather monitoring.

Perry Weather’s real time weather software allows organizations to easily track the heat index and wet bulb globe temperature, as well as other crucial weather metrics in real time. Learn more about our software today and even sign up for a free trial!