How are dewpoint and relative humidity related?

Explanation:

Dew point is the temperature to which air must be cooled to become saturated with water vapor. Relative humidity is the percent of saturation at a given temperature; it depends on moisture content and temperature.  Relative humidity is the amount of moisture actually in the air to the maximum amount that can be present at that temperature. The dew point is the temperature at which a given sample of air will have a relative humidity of 100 percent; hence, the saturation temperature.