By Tammie Painter • Updated March 24, 2022
Conductivity gauges how readily a solution conducts electric current, which is directly tied to the concentration of ions present. By applying a reliable conversion factor, you can estimate ion concentration from a measured conductivity value.
Place the probe of your conductivity meter into the solution and wait for the reading to stabilize. Most modern meters display conductivity in microsiemens (µS) or microohms (µΩ); older models may only show resistivity.
If your meter doesn’t provide conductivity directly, record the resistivity (R) reading. Use Ohm’s law to find conductivity (G):
R = V / I G = 1 / R
Multiply G by 1,000,000 to express it in µS or µΩ.
To estimate the concentration in ppm, multiply the conductivity in µS by 0.64:
ppm = conductivity (µS) × 0.64
Often you’ll need molarity (mol/L) rather than ppm. Since 1 ppm equals 0.001 g of solute per liter, divide the ppm value by the solute’s atomic or molecular weight (g/mol) to obtain molarity:
molarity (mol/L) = ppm ÷ atomic weight (g/mol)
Temperature strongly influences conductivity. For consistent results, measure at 25 °C or use a meter that applies temperature compensation. The conductivity‑to‑concentration conversion works best when the solution contains a single solute; complex mixtures may require more advanced analysis.
