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Converter for humidity of air

temperature: °C
pressure : hPa

%, relative humidity
°C, dew point temperature
°C, dew point difference
hPa, partial pressure
‰v, volume mixing ratio
g/m3, concentration (mass)
molecules/cm3, concentration (molec.)
g/kg, specific humidity (wet air)
g/kg, mixing ratio (dry air)


This is a converter for units of the humidity of air. The equations used may be found on a data sheet (.pdf, 2 pages, 50.5 KiB).

Type the value you want to convert into the field, behind which you find the unit. Click on any empty space in the window or the "calculate" button. Read the result in the other fields. Use the "reset" button to reset your calculation.
For this calculation the temperature in degree Celsius and the pressure in hPa are needed. Without a new entry standard values are used.
After the calculation, the radio button in front of the input value is selected. In the case that you want to use a calculated value for another calculation you may select this value by clicking on the corresponding radio button.

Examples: What is the dew point temperature when the relative humidity is 50 % ? Type "50" into the field in front of "%, relative humidity". Click on any empty space in the window or the "calculate" button. Find your result in the field in front of "°C, dew point temperature" (13.86°C at 25°C air temperature and 1013.25 hPa).

How high is the relative humidity when the air from the example above is cooled down to 15°C ? Since the dewpoint and the volume mixing ratio are kept constant during this cooling, click either on the radio button in front of "°C, dew point temperature" or "‰v, volume mixing ratio". Then change the temperature and click on any empty space in the window or the "calculate" button. Find the result in the field in front of "%, relative humidity" (92.9 %).

Limitations: Supersaturation cannot be calculated with this converter. Therefore calculations above 100 % relative humidity are not possible.
In the calculation of the dew point temperature rounding errors of 0.01 degree might occur.
The calculation of the vapor pressure of H2O is only possible above 0.039 hPa. This corresponds to a vapor pressure above ice at -50°C.

Hints: You may calculate the vapor pressure of water at different temperatures by calculating the partial pressure at 100 % relative humidity. The value of the partial pressure is equal to the vapor pressure in this case. With a temperature change (without condensation or evaporation) the following quantities stay constant: dew point temperature, volume mixing ratio, partial pressure, specific humidity, and mass mixing ratio. With a pressure change volume mixing ratio, specific humidity, and mass mixing ratio stay constant. Therefore you may select the radio button in front of these quantities in the case that you perform a calculation with a temperature or pressure change, respectively.

- Large and small numbers are written exponentially. As example 2.3e5 = 2.3⋅105 = 230000 or 4.5e-5 = 4.5⋅10-5 = 0.000045.
- There is no warranty for the conversion. Cactus2000 is not responsible for damage of any kind caused by wrong results.
- Please send an email if you have suggestions or if you would like to see more conversions to be included.

- A collection of all Cactus2000-converters running offline may be ordered for a price of € 15.-. A test version is available for download for free.

© Bernd Krüger, 05.03.2001

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