Introduction
The Wet Bulb Globe Temperature (WBGT) is a single number that tells you how dangerous the heat really is. Unlike a regular thermometer, WBGT combines air temperature, humidity, wind speed, and sun exposure into one reading.1 This matters because humid, sunny, still air feels far worse than dry, shady, breezy air, even at the same temperature.
This WBGT calculator estimates your heat stress risk. Enter your local weather conditions, and the tool computes a WBGT value and assigns a risk level. It works for both outdoor and indoor settings, in imperial or metric units.
WBGT is a particularly effective indicator of heat stress for active people such as outdoor workers and athletes1, so workers, coaches, and safety managers use it to decide when it is safe to work or play outside. Heat-related illness can cause cramps, exhaustion, and heat stroke. Knowing your WBGT helps you take action (like adding rest breaks, moving to shade, or drinking more water) before anyone gets hurt.
How to Use Our WBGT Calculator
Enter your location, weather conditions, and time of day below. The calculator will estimate the Wet Bulb Globe Temperature (WBGT) and show your heat stress risk level.
Unit System: Choose Imperial (°F, mph, ft) or Metric (°C, m/s, m). All values will convert automatically when you switch.
Latitude and Longitude: Enter the decimal coordinates of your location. These are used to find the sun's position in the sky. You can also press the "Use My Location" button to fill these in automatically.
Date and Time: Enter the current date and time in 24-hour format. The calculator uses these along with your location to figure out how high the sun is and how much solar energy reaches the ground.
UTC Offset: Enter your time zone as hours from UTC. For example, US Eastern is −5 and US Pacific is −8. This is usually filled in for you.
Dry Bulb (Air) Temperature: Enter the current air temperature shown on a standard thermometer. Use °F if Imperial is selected or °C if Metric is selected.
Relative Humidity: Enter the current relative humidity as a percentage from 0 to 100. You can find this from a local weather report or a hygrometer.
Solar Radiation Input: Pick one of three ways to describe sunshine. "Sky Cover" lets you choose a METAR cloud category like Clear or Overcast. "Cloud Cover %" lets you type an exact cloud percentage. "Direct W/m²" lets you enter a measured solar radiation value if you have a pyranometer. With a measured value, the calculator still uses your location, date and time to find the Sun's angle, which splits the reading into direct and diffuse sunlight.
Wind Speed: Enter the current wind speed in mph (Imperial) or m/s (Metric). A small minimum value is applied automatically to keep the math stable. In cold conditions, wind has the opposite effect on perceived temperature.
Measurement Height: Enter the height above ground where the wind speed was measured, in feet (Imperial) or meters (Metric). The calculator adjusts wind to the standard 2-meter reference height used in the WBGT formula.
Press Calculate to see your results. Press Reset to return all fields to their default values.
What Is Wet Bulb Globe Temperature (WBGT)?
Wet Bulb Globe Temperature, or WBGT, is a single number that tells you how dangerous the heat really feels on your body. It indicates the expected heat stress on people, taking into account temperature, humidity, wind speed, sun angle and cloud cover.2 This gives a much better picture of heat stress risk than temperature alone. For a related but simpler measure, see our heat index calculator, which uses only temperature and humidity.
Why WBGT Matters
A hot day with low humidity feels very different from a hot day with high humidity. Humid air makes it harder for your sweat to evaporate, which means your body cannot cool itself as well. Strong sunlight heats your skin directly, and low wind removes less heat from your body. WBGT accounts for all of these factors at once.
ACGIH, the U.S. Armed Forces, and athletic associations use WBGT in their heat guidance and policies, and OSHA's technical manual uses it to assess heat hazards at work.3 When WBGT rises above certain thresholds, workers need longer rest breaks, more water, or may need to stop working outside altogether.
How This Calculator Works
This calculator uses your location, date, time, air temperature, humidity, wind speed, and cloud cover to estimate WBGT. It figures out where the sun is in the sky to estimate how much solar radiation hits the ground. It then calculates two key temperatures: the natural wet bulb temperature, read from a thermometer covered with a moist wick that is not ventilated or shielded, and the globe temperature, read from a probe in the center of a blackened, hollow copper sphere.4 The globe temperature is estimated with the heat balance of a black globe published by the National Weather Service office in Tulsa, which matched measured globe temperatures to within about half a degree Fahrenheit in its tests.5 The sunlight is split into direct and diffuse shares of 0.67 and 0.33, the values Hunter and Minyard used for hazy summer afternoons.4
These values are combined using a standard formula. Outdoors in the sun, the formula is: WBGT = 0.7 × Natural Wet Bulb + 0.2 × Globe Temp + 0.1 × Air Temp.3 Indoors, or outdoors with no solar load, the air temperature term is dropped and the globe temperature gets 30% of the weight.3
Understanding Your Risk Level
Results are sorted into five risk levels from Low to Extreme.
If your WBGT reads 90°F (32.2°C) or higher, conditions are dangerous for almost any outdoor physical activity. Stay hydrated, rest often in shade, and watch for signs of heat illness like dizziness, nausea, or confusion.