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. 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, assigns a risk level, and shows a suggested work-rest schedule based on ACGIH guidelines. It works for both outdoor and indoor settings, in imperial or metric units.
Workers, coaches, athletes, and safety managers use WBGT 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), show your heat stress risk level, and suggest safe work-rest schedules.
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.
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. Unlike a regular thermometer, WBGT combines air temperature, humidity, wind speed, and sun exposure into one reading. 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.
The military, OSHA, athletic trainers, and construction site managers all use WBGT to decide when outdoor work or exercise becomes unsafe. 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, which measures how well sweat can cool you, and the globe temperature, which measures radiant heat from the sun and surroundings.
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. In shade or at night, the air temperature term is dropped and globe temperature gets more weight.
Understanding Your Risk Level
Results are sorted into five risk levels from Low to Extreme. The calculator also shows a work-rest table based on guidelines from the American Conference of Governmental Industrial Hygienists (ACGIH). Light tasks like standing at a desk can continue at higher WBGT values, while heavy tasks like shoveling require rest breaks much sooner.
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.