Wet Bulb Temperature Calculator

This wet bulb temperature calculator tells you how dangerous the heat is right now where you are. Press Use my location or search for a city to see the wet bulb temperature, the WBGT (Wet Bulb Globe Temperature) in the sun and in the shade, a color-coded heat-risk level, work and rest advice and a 48-hour forecast. You can also type in the air temperature and humidity or dew point to calculate the wet bulb temperature yourself.

How to Use the Wet Bulb Temperature Calculator

1. Choose your place. Press Use my location and allow location, or type a city and press Search. The calculator remembers it, so next time it opens with your numbers.
2. Read the result. The wet bulb temperature shows how well sweat can cool you. WBGT adds sunshine and wind; use the sun value outdoors and the shade value under cover.
3. Plan the day. Choose the type of work for work and rest advice, check the sports flag, and look at the 48-hour chart for the hottest hours.
4. Or calculate by hand. Choose Enter values, type the air temperature and relative humidity or dew point, and add the elevation if you are high up.

What Is the Wet Bulb Temperature?

Wrap a wet cloth around a thermometer and let air blow over it: the water evaporates and cools it down. The temperature it settles at is the wet bulb temperature. In dry air the water evaporates fast and the reading drops far below the air temperature. In humid air evaporation slows, and the wet bulb temperature climbs toward the air temperature. Your skin works the same way, which is why a humid 33 °C (91 °F) day can be more dangerous than a dry 43 °C (109 °F) one.

Wet Bulb Temperature Levels

WBGT Heat-Risk Levels

WBGT is the number used for heat safety at work, in sport and in heatstroke alerts. The levels below follow the daily-life guideline used by Japan's heatstroke alert system.

Wet Bulb vs WBGT vs Heat Index

Frequently Asked Questions

What is the wet bulb temperature?

The wet bulb temperature is the lowest temperature air can cool something down to by evaporating water. It combines heat and humidity into one number: in dry air it is far below the air temperature, in very humid air it is close to it. Because sweat cools you the same way, it shows how well your body can cool itself.

What is the wet bulb temperature right now where I am?

Press Use my location, or search for your city. The calculator takes the latest hourly forecast for that place and shows the wet bulb temperature, WBGT in the sun and in the shade, and how they change over the next 48 hours.

What wet bulb temperature is dangerous?

Above about 28 °C (82 °F) hard work and exercise become risky. Research from 2022 found many young, healthy people can no longer keep their core temperature steady at around 31 °C (88 °F). 35 °C (95 °F) is the theoretical limit where the body cannot lose heat at all, even resting in the shade.

What is the difference between wet bulb temperature and WBGT?

The wet bulb temperature only uses heat and humidity. The Wet Bulb Globe Temperature (WBGT) also counts sunshine and wind, so it shows heat stress for people working or playing sport outdoors. WBGT is what OSHA, sports bodies and Japan's heatstroke alerts use.

How is wet bulb temperature different from the heat index?

The heat index is how hot it feels in the shade, and it is usually higher than the air temperature. The wet bulb temperature is lower than the air temperature unless the air is saturated. Both rise with humidity, but the wet bulb temperature is what physiologists use to describe the limits of human cooling.

How do I calculate wet bulb temperature?

Choose Enter values, type the air temperature and either the relative humidity or the dew point, and add your elevation if you are high up. The calculator solves the psychrometric equation including air pressure, which is more accurate than the quick Stull formula, especially at altitude.

How much should outdoor workers rest in the heat?

Pick the type of work and whether workers are used to the heat. The calculator compares the WBGT in the sun with the ACGIH heat stress limits and suggests minutes of work and rest each hour, from working normally to stopping the work outdoors.

How accurate is the WBGT estimate?

It is calculated from the forecast temperature, humidity, wind and cloud cover and the position of the sun, so it is a good guide for planning. A WBGT meter on site measures the real sunshine, ground heat and wind, and is better for official decisions.

Is it free?

Yes. The calculator, the live readings and the 48-hour chart are free with no sign-up. Downloading the 48-hour table as a CSV file for your records is part of the paid plans.