Concentrations of Water Vapor, or Moisture in a gas sample can be expressed in various forms and units:
- Dew/Frost Point Temperature (Td) is the temperature where condensation starts to take place in the form of Liquid Water (Dew) or Ice (Frost). This temperature can be expressed in degree Celsius (°C), degree Fahrenheit (°F) or Kelvin (K).
- Moisture Volume Concentration (ppm) is the proportion of Water Vapor within the gas sample. It is expressed in %v or ppmv (1%v = 10 000 ppmv).
- Relative Humidity (RH) is the proportion of water vapor, compared with the maximum water vapor which could be held in the gas sample at a given temperature and pressure. i.e. a RH of 25% @20°C means that the gas could hold 4 time more water vapor at this temperature without condensation. It is particularly important to differentiate Volume Concentration and Relative Humidity: a Relative Humidity of 32% (@25°C) corresponds to a Moisture volume concentration of 1%.
These 3 ways of indicating Moisture quantities in a gas sample are linked together by well established formulas.
The tool below helps convert between Dew Point, Volume Concentration and Relative Humidity. You may edit any green background input.
The formulas used for the conversions come from General Eastern (Wobum, MA USA). This information is believed to be reliable, but we don’t make any warranty express or implied, as to its accuracy and assume no liability out of its use.