The height at which a parcel of air becomes saturated when lifted dry adiabatically. In essence, a parcel with a humidity of less than 100%, will cool at the dry adiabatic rate of 9.8°C/Km as it lifts from the surface. As it cools, the humidity will increase until it reaches 100%. The altitude at which the parcel reaches saturation is called the lifting condensation level.
Therefore, the height of the LCL is dependent upon the surface moisture. As humidity increases the height of the LCL decreases since it does not need to rise as much to become saturated. Conversely, drier conditions mean the LCL will occur higher in the atmosphere.
To obtain the LCL, start with the surface temperature and follow up the dry adiabat until it cross the saturation mixing ratio of the surface dew point.