Don’t mistake wet bulb for wet bulb globe temperature (WBGT). They are different measurements, but are often – and mistakenly – used interchangeably. Here’s our quick breakdown with all you need to know about everything wet bulb.
What is Wet Bulb Temperature?
To put it simply, Wet Bulb Temperature (WB) is like nature’s version of sweating! It is the coolest temperature the air can reach using evaporative cooling.
In science terms, it is crucial for understanding heat transfer, particularly the cooling effect of evaporation. It tells us how much heat the air can lose through evaporation. The greater the evaporation, the cooler the wet bulb temp, which reflects how much moisture the air can absorb.
How is Wet Bulb Temperature measured?
Wet bulb temperature can be measured by wrapping a thermometer in a wet cloth and exposing it to the air. As water evaporates from the cloth, it cools the thermometer, giving the wet bulb reading.
A fun way to imagine this: if you’ve ever stood in front of a fan right after a shower, you probably noticed that your skin feels a lot cooler.
That’s the same idea behind wet bulb temp—the fan helps evaporate the moisture, which cools you off.
What is Dry Bulb Temperature?
Dry bulb temperature is the standard air temperature we see on weather apps—measured by a regular thermometer exposed to the air but kept dry. It tells us how hot it is without considering moisture in the atmosphere. This is what we commonly see in weather reports.
What’s the difference between Dry bulb and Wet bulb temperature?
The main difference between wet bulb temperature and dry bulb temperature comes down to how they measure heat and how we experience it, especially in relation to humidity and how our bodies cool down.
Dry Bulb Temperature shows the actual air temperature but can be misleading when determining how hot it feels. For example, 90°F in dry Arizona feels different from 90°F in humid Florida.
Dry Bulb Temperature often underestimates how hot it feels when humidity is high. In dry conditions, the dry bulb temperature might accurately reflect the comfort level, as sweat evaporates quickly and cools the body down.
Wet bulb temperature considers both heat and humidity. There’s also a key difference in how air interacts with our bodies. Wet air has more heat capacity, meaning it can store and transfer more heat to or from your body.
Picture being in a sauna versus standing next to a hot campfire.
The dry bulb temperature tells you how hot the fire is, but it won’t tell you how much hotter the sauna feels, because that fire isn’t making you sweat the same way the sauna is!
What’s the difference between wet bulb and WBGT?
Think of wet bulb globe temperature (WBGT) as the new, better heat index or “feels like” temperature. It more holistically measures heat stress on the body by answering: how efficiently can your body produce sweat to cool itself down?
WBGT considers a few factors: wind speed, sun angle, cloud cover, and wet bulb temperature (temperature and relative humidity). Wet bulb temperature is not WBGT, but it is a factor in the WBGT calculation.
So, which one should I use: wet bulb, or wet bulb globe temperature?
If you are concerned with heat stress for outdoor activity, you should almost certainly use wet bulb globe temperature (WBGT) as your measurement.
School athletics (K-12), collegiate athletics, construction, and other outdoor industries commonly use WBGT. If you are an athletic trainer, athletic director, or coach, you know how excessive heat can impact your student athletes.
If you hear a mention of “wet bulb” in the context of heat, they’re probably talking about WBGT.
On the other hand, wet bulb temperature – not WBGT – is more frequently associated with cold-related activities, such as snowmaking and cooling towers.
… But what about “heat index”?
Wet bulb globe temperature (WBGT) serves a similar purpose as heat index – measuring heat stress on the human body – but provides a significantly improved, more accurate measurement than a simple heat index (“feels like” temperature).
Learn more about the heat index here.
Got it. What’s the best way to measure WBGT?
An on-site sensor provides the most accurate and real-time measurement of WBGT. Unless you have an on-site sensor, any apps or websites providing WBGT are simply using a calculated estimate, which can significantly deviate from the actual WBGT.
Perry Weather is the leading weather safety platform for organizations keeping their teams safe in the midst of excessive heat and other environmental conditions. Learn more about how we can help your organization adequately monitor WBGT.
