Heat Stress (WBGT) Calculator

Work out heat stress (wbgt) instantly with clear inputs, formula shown and shareable results.

About Heat Stress (WBGT) Calculator

Wet bulb globe temperature combines humidity, radiant heat and air temperature into one index. Outdoors with solar load it is 0.7 natural wet bulb plus 0.2 globe plus 0.1 dry bulb; indoors the dry bulb term drops out and the globe weighting rises. The heavy weighting on wet bulb reflects that evaporative cooling is the body's main defence.

Formulas

WBGT outdoors

WBGT = 0.7 Tnwb + 0.2 Tg + 0.1 Tdb

WBGT indoors

WBGT = 0.7 Tnwb + 0.3 Tg

Worked example

With the default values below, Heat Stress (WBGT) Calculator returns Wet bulb globe temperature of 29.10. Change any input above and every figure here is recalculated in your browser.

Inputs used

Natural wet bulb temperatureaccepts -10–50 °C: 27 °C
Globe temperatureaccepts -10–80 °C: 35 °C
Dry bulb temperatureaccepts -10–60 °C: 32 °C
Exposure locationone of Outdoors with solar load, Indoors or no solar load: Outdoors with solar load

Results

Wet bulb globe temperature: 29.10 °C
Risk category: High — work rest cycling and acclimatisation required
Screening limit for light work: 31.0 °C
Recommended action: Apply a formal work rest schedule and buddy monitoring

Step by step

1Values used
2WBGT outdoors
3WBGT indoors
4Wet bulb globe temperature= 29.10 °C
5Risk category= High — work rest cycling and acclimatisation required
6Screening limit for light work= 31.0 °C
7Recommended action= Apply a formal work rest schedule and buddy monitoring

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Preliminary estimate only. Heat stress assessment must follow the applicable standard, account for clothing and metabolic rate, and be supervised by a competent person.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Heat stress assessment must follow the applicable standard, account for clothing and metabolic rate, and be supervised by a competent person.

Frequently Asked Questions

How is the Heat Stress (WBGT) figure worked out?

WBGT = 0.7 Tnwb + 0.2 Tg + 0.1 Tdb. Wet bulb globe temperature combines humidity, radiant heat and air temperature into one index.

Why not just use air temperature?

Because a humid 30 °C is far more dangerous than a dry 35 °C. Sweat cannot evaporate in high humidity, so the body loses its main cooling mechanism regardless of air temperature.

What values do I need to enter?

This calculator takes 4 inputs: Natural wet bulb temperature, Globe temperature, Dry bulb temperature, Exposure location. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.