WBGT Calculator (Estimated)

Agarapu Ramesh — Editor and content reviewer
Editorially reviewed Reviewed by Agarapu Ramesh, science educator (chemistry). LinkedIn
Last reviewed: May 2026 | Standard temperature conversion formulas

What this calculator does

This WBGT calculator provides an estimated Wet Bulb Globe Temperature from air temperature and relative humidity. WBGT is widely used as a heat-stress screening metric because it is more relevant than simple air temperature in sunny or high-load outdoor conditions.

Unlike heat index, WBGT is meant to reflect the broader environmental burden on the body. Full WBGT considers wet-bulb temperature, globe temperature, and dry-bulb temperature, which means humidity, radiant heat, airflow, and sunlight all matter. This page uses an approximation, so it should be interpreted as a screening tool rather than a substitute for a measured globe-temperature instrument.

Inputs explained

  • Air temperature: Enter the ambient dry-bulb temperature.
  • Relative humidity: Enter the moisture percentage used to estimate the vapor pressure term.
  • Unit selector: The page converts to Celsius internally because the approximation formula is expressed in metric form.

How it works / method

The engine uses a Bureau of Meteorology-style empirical estimate that converts temperature and humidity into vapor pressure and then applies a linear WBGT approximation. This is useful when you need a fast heat-stress estimate but do not have a dedicated WBGT meter or a full set of radiation and wind observations. Because it is an estimate, it should sit alongside direct weather and exposure context, not replace them.

Formula used

e = (RH / 100) x 6.105 x exp(17.27T / (237.7 + T)); WBGT = 0.567T + 0.393e + 3.94

T is air temperature in C and e is water-vapor pressure in hPa. The page does not solve the full globe-temperature physics, so the result is an estimated WBGT rather than an instrument-grade WBGT observation.

Practical note: WBGT is a heat-stress or workload indicator, not a replacement for direct air temperature. Real-world exposure also depends on solar radiation, clothing, acclimatization, task intensity, and local safety standards.

Wet Bulb Globe Temperature Approximation

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Step-by-step example

Suppose the air temperature is 31 C and the relative humidity is 65 percent. The estimate helps frame how physically demanding those conditions may feel outdoors.

  1. Enter 31 for air temperature.
  2. Enter 65 for relative humidity.
  3. The calculator converts humidity to vapor pressure and then estimates WBGT.
  4. If the resulting value is high, the environment may warrant rest breaks, hydration, shade, or reduced exertion.
  5. The same dry-bulb temperature with lower humidity usually produces a noticeably lower estimate.

Use cases

  • Screening outdoor work or sports conditions before using more formal heat-safety guidance.
  • Comparing sun-exposed hot-weather days when heat index alone may understate environmental stress.
  • Supporting plain-language safety communication in schools, camps, and field operations.
  • Understanding why solar load and humidity can make heat management more complex than a simple thermometer reading suggests.

Assumptions and limitations

  • This page estimates WBGT and does not replace measured globe temperature or full instrument-based WBGT.
  • The approximation does not directly model local radiation, cloud cover, wind profile, clothing, or metabolic work rate.
  • Thresholds vary by region, acclimatization, and the governing guidance for the activity or workplace.
  • Any heat-stress index should be used with hydration, exposure time, and symptom monitoring, not in isolation.

If you only want a shaded comfort index, use heat index instead. If you need compliance or formal exposure management, use measured WBGT and the relevant organizational standard.

WBGT Calculator and Heat Stress Index

Use the wbgt calculator, wbgt index calculator, wbgt temperature calculator, or wet bulb temperature calculator when heat, humidity, sun, and workload matter more than air temperature alone. OSHA recommends on-site WBGT measurement for workplace heat assessment because WBGT accounts for humidity, radiant heat, air temperature, and air movement.

The wbgt formula is usually outdoor WBGT = 0.7 natural wet bulb + 0.2 globe temperature + 0.1 dry bulb temperature. Indoor or shaded WBGT uses 0.7 natural wet bulb + 0.3 globe temperature. That also covers wbgt calculation, wbgt index calculation, wbgt calculator formula, wbgt calc, heat stress index wbgt, calculador wbgt, and wbgt在线计算.

Canadian Humidex Formula

Use a humidex calculator or humidex calculator canada when the Canadian apparent-temperature scale is requested. A common humidex formula is Humidex = T + 0.5555 × (e - 10), where T is air temperature in Celsius and e is vapour pressure in hPa. This helps with humidex from rh and temp calculator, humidex calculation chart, and how to calculate humidex using temp & humidity %.

Stull Wet Bulb Formula

Stull's equation estimates wet-bulb temperature from air temperature and relative humidity at standard sea-level pressure. The 2011 paper gives a fast approximation for many weather ranges, useful when you need roland stull wet bulb temperature fomula or wet bulb temperature aceton approximation wording in field notes.

Frequently Asked Questions

Outdoor with sun: WBGT = 0.7Tw + 0.2Tg + 0.1Td, where Tw is natural wet bulb, Tg is globe temperature, Td is dry bulb. Indoor or shaded: WBGT = 0.7Tw + 0.3Tg, dropping the dry bulb because solar load is absent. The weights are not arbitrary — they come from research showing humidity contributes about 70%, radiant heat 20–30%, and air temperature only 10% to total heat-stress risk. Without instruments, estimated WBGT formulas use temperature, humidity, wind, and solar irradiance instead.
The full outdoor form is WBGT = 0.7 × natural wet bulb + 0.2 × globe + 0.1 × dry bulb, all in °C. Natural wet bulb captures evaporative cooling load. Globe temperature, measured inside a black-painted hollow sphere, captures radiant heating from sun and surroundings. Dry bulb is just the standard air temperature. The 7:2:1 weighting reflects how the human body actually loads up under heat: humidity dominates, radiation matters in sun, and air temperature is the smallest contributor.
ACGIH and ISO 7243 set work-rest ratios by WBGT. Below 25°C is generally safe for most labour. 25–28°C light work continuously, moderate work needs breaks. 28–30°C limits get tighter. Above 30°C even acclimatised, fit workers need substantial rest. Above 32°C, very hard physical work is unsafe. These are guidelines — clothing, hydration, age, fitness, and acclimatisation status all shift the practical line. Always follow your country's occupational safety regulations rather than a generic chart.
Above 30°C WBGT is the threshold most occupational standards flag for serious heat-stress risk. Above 32°C, heat illness becomes likely even for fit, acclimatised workers without rest cycles. Sport governing bodies — football, military, marathon — typically suspend or modify activities above 32°C WBGT. Above 33°C, all but essential work should stop. These limits are tighter than they look on a thermometer because WBGT already accounts for humidity and sun. Defer to OSHA, ACGIH, or your local occupational-health authority for legal limits.
Use Liljegren's algorithm or one of its derivatives. Inputs are air temperature, relative humidity, wind speed, solar irradiance, and location/time for sun-angle calculations. The algorithm reconstructs natural wet bulb and globe temperature analytically, then applies the standard weighted sum. Estimated WBGT typically agrees with measured WBGT to within about 1°C under good conditions. For decision-making in casual settings — sport, school PE, outdoor events — estimated WBGT is fine. For OSHA compliance and legal documentation, use a calibrated instrument.
Direct sun adds significant solar load, captured by the globe temperature term. On a clear summer noon, the globe thermometer can read 6–8°C higher than air temperature, pushing outdoor WBGT well above the indoor value for the same air conditions. That is why athletes who train indoors and then compete outdoors get caught out. The solar contribution depends on cloud cover, sun angle, surface reflectivity, and humidity. Estimated WBGT formulas need solar irradiance in W/m2 to capture this properly.
Wet bulb temperature is a single thermometer reading — what an evaporatively cooled bulb settles at — and it captures only humidity and air temperature. WBGT is a composite index: 70% wet bulb plus 30% globe (indoor) or 70-20-10 with dry bulb (outdoor). WBGT captures radiation and air temperature on top of evaporative cooling, so it is a fuller picture of heat stress on a working human. Wet bulb is one input; WBGT is the engineered output you actually use.
Location coordinates and date/time so the algorithm can compute solar zenith angle. Air temperature, relative humidity (or dew point), wind speed, and total solar irradiance in W/m2. If you have a calibrated globe thermometer and natural wet bulb sensor, you can skip estimation and use direct readings. OSHA does not specify a single legal formula but accepts ISO 7243-style WBGT and validated estimation methods. Document your instruments, calibration dates, and method — that paper trail matters more than the exact algorithm you choose.

Sources & references

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