The conductivity of a liquid is measured using special conductivity sensors. The unit of conductivity is siemen/cm. A siemen is 1/ohm. The unit of conductance is sometimes referred to mho (ohm written in reverse).

The conductance is usually a very low value for conducting liquids such as water. It will be of the order of a millionth of a siemen, in microsiemens. Highly pure water, for instance, will have a conductivity of 1microsiemen/cm.

Measurement of conductivity

Conductivity is measured by measuring the conductivity of a liquid between two electrodes whose area and distance between each other is fixed. This is known as a cell constant.

A cell constant of 1 implies that the electrodes will have a surface area of 1 cm2 and will be spaced 1 cm apart.