How this calculator works
Stull approximation estimates wet-bulb temperature from Celsius dry bulb and percentage RH at standard sea-level pressure. This tool restricts its use to 0 through 50 C and 5 through 100% RH, avoiding the cold dry corner of the published fit; saturation is handled exactly. WBGT formulas require a natural wet bulb and a black globe measurement. When using the Stull estimate, the WBGT results are exploratory approximations because a ventilated thermodynamic estimate does not reproduce a natural wet bulb under radiation and wind. Select measured natural wet bulb for the instrument-based combination. No exposure limit or clinical interpretation is calculated.
Formula
Tw(C) approximately equals T atan[0.151977 sqrt(RH+8.313659)] + atan(T+RH) - atan(RH-1.676331) + 0.00391838 RH^1.5 atan(0.023101 RH) - 4.686035. WBGT_out = 0.7 T_nwb+0.2 T_globe+0.1 T_dry; WBGT_in = 0.7 T_nwb+0.3 T_globe.
Worked example
At 20 C and 50% RH, the Stull wet-bulb estimate is about 13.69934 C. If dry bulb, natural wet bulb and globe are all 30 C, both WBGT combinations equal 30 C.
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Frequently asked questions
Is wet bulb the same as dew point?
No. Evaporation cools a wetted bulb, while dew point describes saturation at the current vapour pressure.
Is the wet-bulb depression a temperature?
It is a temperature difference. A difference of 1 K equals 1 C degree but 1.8 F degrees.
Can an estimated wet bulb replace a natural wet-bulb sensor for WBGT?
Not for an instrument-based assessment. Radiation and airflow affect natural wet-bulb readings; the estimate is provided only as an exploratory comparison.