Dew Point Temperature Calculation

The dew point is the temperature at which air is saturated with water vapor, at which water droplets start to condense and form dew on surfaces.

It also may defines - 

The dew point or dew point temperature of a gas is the temperature at which the water vapor or low-boiling hydrocarbon derivatives contained in the gas is transformed into the liquid state.

When air has reached the dew-point temperature at a particular pressure, the water vapor in the air is in equilibrium with liquid water. A higher dew point temperature means that the air is more humid, while lower dew point temperature indicates that the air is drier.

Dew Point Calculation Formula

If you know the observed temperature and relative humidity the following formula can apply for a simpler calculation that gives an approximation of dew point temperature:

Td = T - ((100 - RH)/5)


  • Td = dew point temperature (in degrees Celsius), 
  • T = observed temperature (in degrees Celsius), and 
  • RH = relative humidity (in percent). Apparently this relationship is fairly accurate for relative humidity values above 50%.

The dew point temperature can also be calculated using the following formula:

Td = 243.04 * (ln(RH/100) + ((17.625 * T) / (243.04 + T))) / (17.625 - ln(RH/100) - ((17.625 * T) / (243.04 + T)))


  • Td = dew point temperature (°C)
  • RH = relative humidity (%)
  • T = air temperature (°C)

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