Quick answer
The wet-bulb temperature is estimated from temperature and relative humidity with the Stull (2011) empirical fit. Air at 20 °C and 50% RH has a wet-bulb temperature of 13.7 °C (56.66 °F).
Enter the air temperature and relative humidity. The calculator returns the wet-bulb temperature in °C and °F.
Related tools: Relative Humidity Calculator: Relative humidity from air temperature and dew point. Air Density Calculator: Density of moist air from pressure, temperature and humidity. Absolute Humidity Calculator: Water vapor content of air in grams per cubic meter.
How to use the Wet Bulb Temperature Calculator
- Enter air temperature (°C) (between -20 and 50).
- Enter relative humidity (%) (between 5 and 99).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Air temperature | A number, in °C | ≥ -20, ≤ 50 |
| Relative humidity | A number, in % | ≥ 5, ≤ 99 |
Formula and method
Formula
Stull (2011) empirical fit of T_w from T and RH
IEEE-754 double precision; shown to the decimals indicated.
Valid for −20 to 50 °C and 5 to 99% humidity at sea-level pressure, with an error under about 1 °C.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Air temperature = 20; Relative humidity = 50.
| Result | Value |
|---|---|
| Wet-bulb temperature | 13.7°C |
| In °F | 56.66 |
Example 2
Inputs: Air temperature = 30; Relative humidity = 70.
| Result | Value |
|---|---|
| Wet-bulb temperature | 25.6°C |
| In °F | 78.07 |
Example 3
Inputs: Air temperature = 5; Relative humidity = 90.
| Result | Value |
|---|---|
| Wet-bulb temperature | 3.99°C |
| In °F | 39.19 |
The first line is the headline result (wet-bulb temperature). Below it the wet Bulb Temperature Calculator lists in °F, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
What it means
The wet-bulb temperature is the lowest temperature reached by evaporative cooling, which a wet thermometer shows. It sets the limit for evaporative coolers and for human heat tolerance: a wet bulb above about 35 °C is lethal to humans in hours.
Valid range
The fit is valid for roughly 5 to 99% RH and −20 to 50 °C; outside the valid range it is unreliable. Wet-bulb is lower than dry-bulb unless the air is saturated.
How the result changes with air temperature
Holding every other input at the first worked example, this table changes only air temperature. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Air temperature | Wet-bulb temperature | In °F |
|---|---|---|
| 10 | 5.1°C | 41.18 |
| 20 | 13.7°C | 56.66 |
| 40 | 30.89°C | 87.61 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Air temperature: entering "60" shows "Air temperature must be at most 50." beside that field and no result.
- Relative humidity: entering "2" shows "Relative humidity must be at least 5." beside that field and no result.
Choosing between the Wet Bulb Temperature Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Relative Humidity Calculator](/science/relative-humidity/) | air temperature and dew point | Relative humidity |
| [Air Density Calculator](/science/air-density/) | pressure, temperature and relative humidity | Air density |
| [Absolute Humidity Calculator](/science/absolute-humidity/) | temperature and relative humidity | Absolute humidity |
| [Temperature Converter](/converters/temperature-converter/) | value, from and to | Celsius (°C) → Fahrenheit (°F) |
| [Oven Temperature Converter](/cooking/oven-temperature-calculator/) | convert | Temperature |
Background: environment and acoustics
Decibels are a logarithmic scale, so sound levels cannot be added arithmetically: two equal sources raise the level by about 3 dB, not double it. Environmental and emissions results depend on the factors behind them (for example the US EPA's equivalency factors), which are averages for a country, fuel and year.
Use the result to compare scenarios rather than as a measured value.
Assumptions and limitations
- Outside the valid range the fit is unreliable
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for air temperature and relative humidity to confirm this.
Frequently asked questions
What is wet-bulb globe temperature?
A heat-stress index that adds sun and wind.
Why is wet bulb lower?
Evaporation cools the wet bulb.
When are they equal?
Wet-bulb and air temperature are equal at 100% relative humidity, because no evaporation can occur.
What does the Wet Bulb Temperature Calculator calculate?
Wet-bulb temperature from air temperature and relative humidity (Stull's formula). It returns Wet-bulb temperature and In °F.
What formula does the Wet Bulb Temperature Calculator use?
Stull (2011) empirical fit of T_w from T and RH. Valid for −20 to 50 °C and 5 to 99% humidity at sea-level pressure, with an error under about 1 °C.
What do I need to enter in the wet Bulb Temperature Calculator?
You enter Air temperature (°C) and Relative humidity (%).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Outside the valid range the fit is unreliable.
What is an example of a wet Bulb Temperature result?
With air temperature 20 and relative humidity 50, the wet-bulb temperature is 13.7°C.
Where does the method come from?
The method follows: Stull R, Wet-bulb temperature from relative humidity and air temperature, J. Appl. Meteor. Climatol. 50 (2011) 2267.
Related calculators
- Relative Humidity Calculator — Relative humidity from air temperature and dew point.
- Air Density Calculator — Density of moist air from pressure, temperature and humidity.
- Absolute Humidity Calculator — Water vapor content of air in grams per cubic meter.
- Temperature Converter — Celsius, Fahrenheit, Kelvin and Rankine.
- Dew Point Calculator — Dew point from temperature and relative humidity.
Sources
- Stull R, Wet-bulb temperature from relative humidity and air temperature, J. Appl. Meteor. Climatol. 50 (2011) 2267
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.