MasterTool

Wet Bulb Calculator

Calculate wet bulb instantly in your browser — the published formula, worked locally with no data sent anywhere.

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What this tool does

Calculate wet bulb instantly in your browser — the published formula, worked locally with no data sent anywhere. Stull's formula is accurate to about ±0.3 °C for most conditions (RH 5–99%, T −20 to 50 °C) at standard pressure. A true psychrometer reading also depends slightly on pressure and ventilation.

How to use the Wet Bulb Calculator

  1. Enter or select air temperature (°c).
  2. Enter or select relative humidity (%).
  3. Enter or select air pressure (hpa, for psychrometric check).
  4. Read the calculated result; change any measurement to compare alternatives.

Formula

Stull (2011) approximation: Tw = T·atan(0.151977·√(RH + 8.313659)) + atan(T + RH) − atan(RH − 1.676331) + 0.00391838·RH^1.5·atan(0.023101·RH) − 4.686035, with T in °C and RH in %.
temp
Air temperature (°C)
rh
Relative humidity (%)
pressure
Air pressure (hPa, for psychrometric check)

Stull's formula is accurate to about ±0.3 °C for most conditions (RH 5–99%, T −20 to 50 °C) at standard pressure. A true psychrometer reading also depends slightly on pressure and ventilation.

Worked example

For wet bulb calculator, the following measurements illustrate the exact method: Air temperature (°C): 30; Relative humidity (%): 50; Air pressure (hPa, for psychrometric check): 1013.25.

Inputs

  • Air temperature (°C)30
  • Relative humidity (%)50
  • Air pressure (hPa, for psychrometric check)1013.25

Result

  • Wet bulb temperature (°C)22.3
  • Wet bulb temperature (°F)72.13
  • Wet bulb depression (°C)7.7
  • Heat-stress guidanceCaution — monitor during hard exertion

Results explained

Wet bulb temperature (°C)
Wet bulb temperature (°C) from the formula above. Stull's formula is accurate to about ±0.3 °C for most conditions (RH 5–99%, T −20 to 50 °C) at standard pressure. A true psychrometer reading also depends slightly on pressure and ventilation.
Wet bulb temperature (°F)
Wet bulb temperature (°F) from the formula above. Stull's formula is accurate to about ±0.3 °C for most conditions (RH 5–99%, T −20 to 50 °C) at standard pressure. A true psychrometer reading also depends slightly on pressure and ventilation.
Wet bulb depression (°C)
Wet bulb depression (°C) from the formula above. Stull's formula is accurate to about ±0.3 °C for most conditions (RH 5–99%, T −20 to 50 °C) at standard pressure. A true psychrometer reading also depends slightly on pressure and ventilation.
Heat-stress guidance
Heat-stress guidance from the formula above. Stull's formula is accurate to about ±0.3 °C for most conditions (RH 5–99%, T −20 to 50 °C) at standard pressure. A true psychrometer reading also depends slightly on pressure and ventilation.

Frequently asked questions

Stull (2011) approximation: Tw = T·atan(0.151977·√(RH + 8.313659)) + atan(T + RH) − atan(RH − 1.676331) + 0.00391838·RH^1.5·atan(0.023101·RH) − 4.686035, with T in °C and RH in %.

Stull's formula is accurate to about ±0.3 °C for most conditions (RH 5–99%, T −20 to 50 °C) at standard pressure. A true psychrometer reading also depends slightly on pressure and ventilation.

At a wet bulb of 35 °C, air is saturated at skin temperature, so sweat cannot evaporate at all. Even a resting, hydrated person in the shade then gains heat faster than they can shed it.

Every field is labelled with its unit — enter values in exactly the labelled unit and read the result in the labelled output unit. Fields with a unit symbol also support the site-wide imperial/metric switch, which converts before the formula runs.

It uses double-precision arithmetic and the published constants and formulas named on this page. The last displayed digit may be rounded, and real conditions can differ from the idealized model described in the assumptions.

Yes. Every calculation runs entirely in your browser; nothing you enter is uploaded, stored or shared.