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Wet Bulb Temperature Calculator

Work out wet bulb temperature instantly with clear inputs, formula shown and shareable results.

About Wet Bulb Temperature Calculator

Wet bulb temperature is the lowest temperature reachable by evaporative cooling, computed here with Stull's empirical fit. At 32 C and 70% humidity it is about 27.5 C. It matters because human cooling depends on sweat evaporation: a wet bulb of 35 C is the theoretical survivability limit, since the body can no longer shed metabolic heat at all.

Formulas

Stull approximation

Tw = 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

Wet bulb depression

depression = dry bulb - wet bulb

Worked example

With the default values below, Wet Bulb Temperature Calculator returns Wet Bulb Temperature of 27.46. Change any input above and every figure here is recalculated in your browser.

Inputs used

Air temperature
32 C
Relative humidityaccepts 5–99 %
70 %

Results

Wet Bulb Temperature
27.46 C
Wet Bulb Depression
4.54 C
Heat Stress Assessment
Caution during heavy work
Saturation Vapour Pressure
47.451 hPa

Step by step

  1. 1Values used
  2. 2Stull approximation
  3. 3Wet bulb depression
  4. 4Wet Bulb Temperature= 27.46 C
  5. 5Wet Bulb Depression= 4.54 C
  6. 6Heat Stress Assessment= Caution during heavy work
  7. 7Saturation Vapour Pressure= 47.451 hPa

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is a 35 C wet bulb fatal?

Because skin sits near 35 C, so no evaporative gradient remains. Metabolic heat then accumulates regardless of shade, water or fanning.

How accurate is the Stull formula?

Within about 0.3 C for humidity between 5 and 99% at normal pressures - ample for heat stress assessment.

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