What does WBGT stand for?

WBGT stands for Wet Bulb Globe Temperature. People sometimes call it the WBGT index, although the final word in the acronym already refers to temperature.

How is the WBGT index calculated?

A standard outdoor measurement combines 70% natural wet-bulb temperature, 20% globe temperature and 10% dry-bulb temperature. Forecast-based estimates model some of those inputs and are not equivalent to an on-site instrument reading.

Is WBGT the same as heat index?

No. Heat index uses air temperature and humidity under shaded, light-wind assumptions. WBGT is intended to incorporate moisture, radiant heat, air temperature and air movement, so the values and thresholds are not interchangeable.

HeatGuard field guide

Wet Bulb Globe Temperature (WBGT Index): a practical guide

Wet Bulb Globe Temperature—often searched for as the WBGT index—is a heat-stress measure designed for people who are active outdoors. It combines several parts of the environment that affect the body's ability to shed heat instead of describing air temperature alone.

Written and reviewed by the HeatGuard Editorial TeamLast reviewed August 20, 2026How we review content

Estimated WBGT planning reference

WBGT index chart: HeatGuard planning bands

These are HeatGuard's general planning bands for an estimated WBGT. They are not measured WBGT values or official work-rest limits and must not replace thresholds issued for a workplace, school, team or governing body.

Below 23°C

Low

Routine precautions

23–25.9°C

Moderate

Add breaks and monitor

26–27.9°C

High

Shorten hard efforts

28–29.9°C

Very high

Limit strenuous activity

30°C+

Extreme

Use the most conservative plan

What WBGT captures

WBGT accounts for air temperature, moisture, radiant heat and air movement. Sweat must evaporate to cool the body, direct sun adds radiant load, and wind can change how quickly heat leaves the skin.

A standard outdoor instrument combines a natural wet-bulb sensor, a black-globe sensor and a dry-bulb sensor. With solar load, the common equation is 0.7 × natural wet bulb + 0.2 × globe temperature + 0.1 × dry bulb temperature.

Natural wet bulb reflects evaporative cooling.
Globe temperature reflects radiant heat.
Dry bulb represents ambient air temperature.

Measured and estimated are not interchangeable

A meter measures conditions at a specific place. A weather-based estimate models WBGT from forecast variables. Estimates help with advance planning, but may miss shade, artificial turf, asphalt, nearby buildings, clothing and local wind.

HeatGuard labels modeled values as estimated. If a league, employer or governing body requires an on-site measurement, use its required instrument and protocol.

How to use a reading

There is no universal cutoff for every person and activity. Limits depend on workload, clothing, acclimatization and the rules governing the activity. Start with the applicable protocol, then use hourly conditions to choose a lower-load window.

Reduce intensity, increase recovery, use shade and watch the individual—not only the number. Confusion, fainting or suspected heat stroke requires immediate emergency action.

Use HeatGuard to compare hours, not certify compliance.
Treat direct sun and protective equipment as added load.
Give new or returning participants time to acclimatize.

How to read a WBGT chart

A WBGT chart maps a measured or estimated value to an action band. The raw value is usually shown in Celsius and will be lower than a familiar Fahrenheit heat-index number. Compare the value only with a chart designed for the activity and population in question.

HeatGuard's chart uses general planning bands to make the forecast easier to scan. It is not an official sports, military or workplace table. Protocols may change limits for workload, clothing, acclimatization or local policy.

Confirm whether the chart expects °C or °F.
Confirm whether the reading is measured or modeled.
Apply the governing protocol, not a generic internet threshold.

Frequently asked questions

What does WBGT stand for?: WBGT stands for Wet Bulb Globe Temperature. People sometimes call it the WBGT index, although the final word in the acronym already refers to temperature.
How is the WBGT index calculated?: A standard outdoor measurement combines 70% natural wet-bulb temperature, 20% globe temperature and 10% dry-bulb temperature. Forecast-based estimates model some of those inputs and are not equivalent to an on-site instrument reading.
Is WBGT the same as heat index?: No. Heat index uses air temperature and humidity under shaded, light-wind assumptions. WBGT is intended to incorporate moisture, radiant heat, air temperature and air movement, so the values and thresholds are not interchangeable.

Primary sources

Continue planning

This guide provides environmental planning information. It is not medical advice, an emergency service, or a substitute for an applicable workplace, school, league or governing-body protocol.

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