Rex says
Same equations the textbooks use — just way less awkward. Pop in your stats and I'll tell you what the number actually means for you.
Try a scenario
Click to load — tweak from there.Inputs
Result
Estimated WBGT
84.5
WBGT (°C)
29.2
Activity flag guidance
Yellow — moderate risk
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter air temperature (°F).
- 2Enter relative humidity (%).
- 3Enter sun exposure.
- 4Read your estimated wbgt on the right — it updates as you type.
- 5Hit Share to keep the scenario or send it to someone.
About this calculator
Wet Bulb Globe Temperature (WBGT) is the standard heat stress index used by the military, OSHA, and high school athletic associations because unlike heat index, it accounts for direct solar radiation and wind in addition to humidity and air temperature. This calculator uses a simplified approximation that estimates WBGT from air temperature, relative humidity, and whether you're in direct sun or shade, mapping the result onto standard flag-based activity guidance (green/yellow/orange/red/black) used in sports heat acclimatization protocols. A true WBGT reading requires a specialized meter with a black globe thermometer, so treat this as a planning estimate, not a substitute for an on-site instrument when heat stress liability is on the line.
Worked example
Using the values the calculator loads with:
Inputs
- Air temperature: 92 °F
- Relative humidity: 55 %
- Sun exposure: Full direct sun
Results
- Estimated WBGT: 84.5
- WBGT (°C): 29.2
- Activity flag guidance: Yellow — moderate risk
What each field means
Inputs
- Air temperature (°F)
- The air temperature used in the calculation, measured in °F. Starts at 92 °F so you have a working example on load. Accepted range: 60–120 °F.
- Relative humidity (%)
- The relative humidity used in the calculation, measured in %. Starts at 55 % so you have a working example on load. Accepted range: 5–100 %.
- Sun exposure
- Pick the option that matches your situation — the maths changes per option. Choices: Full direct sun, Partial shade, Full shade.
Results
- Estimated WBGT
- Returned as a whole number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- WBGT (°C)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Activity flag guidance
- Returned as a plain value. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How is WBGT different from heat index?
Heat index assumes shade and light wind and is calibrated for general public reporting. WBGT adds direct solar radiation via a black globe thermometer reading and is designed specifically for people exercising or working outdoors in the sun, which is why it's the standard for sports and military heat safety protocols instead of heat index.
What do the flag colors mean for practice or work?
Most high school athletic association guidelines start mandatory water breaks and reduced equipment at yellow, require significant activity modification at orange, limit practice to light activity with frequent breaks at red, and cancel outdoor activity entirely at black flag conditions.
Can I get a truly accurate WBGT without a meter?
Not precisely — this calculator is a documented approximation (Stull's formula for natural wet bulb temperature plus an estimated globe temperature boost for sun exposure), useful for planning, but organizations with heat safety liability should use an actual WBGT meter with a real black globe sensor on site.
Why does wind speed matter for real WBGT but isn't in this simplified version?
Wind affects both the natural wet bulb and black globe readings in a true WBGT meter — more wind cools the globe and speeds evaporation. This simplified estimate omits wind for usability, so treat results as slightly conservative (underestimating cooling) in windy conditions.
Accuracy and limitations
- Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.
- Results do not account for medical conditions, medication, or pregnancy.
- Use this as a directional reference, not a diagnosis — talk to a clinician before acting on it.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). WBGT Heat Stress Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/wbgt-heat-stress
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/wbgt-heat-stress" target="_blank" rel="noopener">WBGT Heat Stress Calculator — RevenueLab</a> (2026).</p>
Source: [WBGT Heat Stress Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/wbgt-heat-stress) (2026).