Wet-bulb temperature describes cooling possible through evaporation under specified conditions. Evaporation cools a wetted thermometer sensor; humid air leaves less room for that cooling.
Not medical advice.
A worked evaporation example
In unsaturated air, evaporation normally lowers wet bulb below dry-bulb air temperature. At 100% relative humidity the two temperatures are equal; this calculator handles saturation separately rather than extrapolating Stull's formula.
Wet bulb, heat index and WBGT
Wet bulb
Evaporative cooling. This calculator estimates it from air temperature and RH at standard pressure; it does not measure a natural wet-bulb sensor.
Heat index
A feels-like estimate using air temperature and RH, assuming shade and light wind. Its risk bands do not apply to wet bulb.
Read the heat-index guideWBGT
Wet-bulb globe temperature combines natural wet bulb and globe readings, plus air temperature for the sun equation. Wet bulb alone is not WBGT.
Explore WBGT methodsHow to read an estimate
- Enter air temperature and relative humidity from the same place and time in the wet-bulb calculator.
- Check the pressure assumption and supported input range. The answer is an approximation, not an instrument reading.
- Keep the concepts separate: wet bulb involves evaporation; dew point describes saturation reached by cooling air without changing moisture content.
- Follow official local and workplace guidance. Do not turn this environmental estimate into a personal tolerance limit or survival timer.
Check the assumptions
- Pressure: the estimate assumes standard sea-level pressure, 101.325 kPa. Altitude is not accounted for.
- Site range: 0–50°C (32–122°F) and 5–99% RH, plus the separate 100% saturation case. Unsupported inputs are rejected, not silently clamped.
- Not measured WBGT: calculated wet bulb is not interchangeable with a natural wet-bulb sensor reading in WBGT equipment.
- Not a safety clearance: sunlight, exertion, clothing and personal circumstances are not assessed.
Frequently asked questions
Is wet bulb the same as dew point?
No. Wet bulb involves evaporative cooling. Dew point describes the temperature at which air reaches saturation when cooled without changing its moisture content.
Can I use this estimate as a natural wet-bulb measurement for WBGT?
No. This Stull estimate is not a reading from a natural wet-bulb sensor. The WBGT tool labels its shade-only approximation separately from measured-input modes.
Can wet bulb predict a safe time outdoors?
No. Environmental conditions alone cannot establish a personal safe exposure time. Follow official local guidance rather than a universal threshold.
Method and next steps
The estimate uses Stull's 2011 approximation; UCAR documents the method. The calculator includes the equation and scope; see OSHA's heat-hazard guidance for workplace context.
Reviewed 6 November 2026. Not medical advice.