The electrical conductivity translates the ability of an aqueous solution to drive the electric current. The commonly used unit of measurement is the Siemens/cm (S/cm) often expressed in Microsiemens/cm (ΜS/cm) or milliSiemens (MS/cm). Conductivity is directly proportional to the amount of solids dissolved in water. Thus, the higher the concentration of dissolved solids, the higher the conductivity will be.

Generally, the ratio of conductivity to ionic concentration is expressed by approximation as follows:

µS/cm = 1 ppm (part per million)

where 1 ppm = 1 mg/L is the dissolved solid concentration.

Some conductimeters directly convert conductivity to PPM and thus provide a direct reading of the total dissolved solids concentration.