Wet Bulb Temperature Calculator

How to use

1. 1Pick your unit system: Fahrenheit or Celsius. The result panel always shows both units regardless.
2. 2Choose how you want to enter humidity: Relative humidity % for the most common case, or Dew point when that is the reading you already have.
3. 3Type the air temperature and humidity. The wet-bulb temperature, simplified WBGT, and human-tolerance band update on every keystroke.
4. 4Use the quick-pick humidity chips (20 percent, 30 percent, and so on up to 90 percent) to flip through scenarios fast, or read the full wet-bulb reference table at the bottom for any combination.
5. 5Watch the validity notes: if your air temperature drifts below -20 C, above 50 C, or your humidity drifts below 5 percent or above 99 percent, the Stull regression is extrapolated and the tool flags it.
6. 6Click Copy report to grab a plain-text summary of the air temperature, humidity, dew point, wet-bulb temperature, simplified WBGT, and tolerance band for a ticket, safety briefing, or training log.

About this tool

Wet Bulb Temperature Calculator turns an air temperature plus a humidity reading into the wet-bulb temperature, the lowest temperature a wet thermometer (and a sweating human body) can reach by evaporation in that air. The calculation uses Roland Stull's 2011 closed-form expression from the Journal of Applied Meteorology and Climatology, which solves the wet-bulb temperature from air temperature and relative humidity without an iterative psychrometric solver, with RMS error around 0.3 C across its validity envelope of -20 C to 50 C and 5 to 99 percent humidity at standard sea-level pressure. You can type the air temperature and humidity in either Fahrenheit or Celsius; the result panel reports both units, the relative humidity, the dew point (derived through Magnus-Tetens), the evaporative cooling potential (how much cooler the wet bulb is than the dry bulb), the water vapor pressure used downstream, and a simplified outdoor Wet-Bulb Globe Temperature using the Australian Bureau of Meteorology approximation (0.567 * T + 0.393 * e + 3.94, where e is water vapor pressure in hPa). Switch the humidity input to dew point and the tool derives relative humidity before running Stull, which is useful when the only thing you have is a temperature and dew point pair from a weather report or aviation METAR. The result is colour-coded against seven human-tolerance bands (Comfortable below 20 C, Uncomfortable 20 to 25 C, Moderate heat stress 25 to 28 C, High heat stress 28 to 31 C, Very high heat stress 31 to 33 C, Extreme heat stress 33 to 35 C, and Survival limit exceeded above 35 C) drawn from Sherwood and Huber (2010) and the Vecellio et al. (2022) critical wet-bulb research, and against five ACGIH-style WBGT work-rest categories so outdoor workers and athletes can plan rest cycles. A full wet-bulb reference chart at the bottom shows every cell from 20 C to 45 C air temperature across 20 to 100 percent relative humidity, with the same colour bands, so you can sanity-check a single point against a wider grid. Useful for outdoor workers, athletes, coaches, parents, gardeners, HVAC and cooling-tower engineers sizing evaporative systems, climate researchers, public-health planners tracking dangerous heat days, anyone who has typed wet bulb 35 c, what is my wet bulb today, or heat stress threshold into a search bar, and anyone who needs the wet-bulb temperature without installing a Python notebook. All math runs locally in your browser using standard JavaScript arithmetic; the temperatures and humidity values you type here never leave your device.

Free to use. Works in your browser. No signup, no login.