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To measure the resistance or conductivity of a sample, the current and voltage across the electrodes of a conductivity cell must be measured. Conductance (G) is defined as the reciprocal of resistance:

G = 1 / R = I / V

The value of conductance depends on the geometry of the electrode plates and is represented by the cell constant (K), which is the ratio of the distance between the electrodes (L) to the surface area of the electrode plates (A):

K = L / A

どこでだ：

• K — Cell constant of the conductivity electrode
• A — Effective area of the electrode plates
• L — Distance between the electrode plates

This value is referred to as the cell constant, and it can be calculated from the electrode’s geometric dimensions. For example, when two square electrode plates each have an area of 1 cm² and are spaced 1 cm apart, the cell constant K = 1 cm⁻¹.
If the measured conductance (G) using this electrode is 1000 μS, then the conductivity of the solution is:

κ = 1000 μS/cm

Conductance can be converted into standardized conductivity (κ), which is independent of the electrode configuration. This is done by multiplying the conductance by the cell constant:

κ = G × L / A = G × K