Convert electrical conductivity between S/m, S/cm, mS/cm and µS/cm — common in water-quality testing.
Electricity • 7 units
All 7 units on the Electric Conductivity Converter are defined against the Siemens/meter (S/m), so each result is one conversion factor away from a single reference rather than the end of a chain of roundings.
The conversion this page is most often opened for is ready before you type anything: 1 µS/cm = 0.001 mS/cm. Change either side and every row in the table recalculates with it.
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Conductivity readings move between scales that differ by a factor of 100, and this page defaults to the pair that causes most of the trouble: microsiemens per centimetre to millisiemens per centimetre. One mS/cm is 1,000 µS/cm, and because both are centimetre-based rather than SI, converting either into siemens per metre means dividing by ten — 1 mS/cm is 0.1 S/m. Meter displays rarely state which of the three they are showing, and a reading transcribed without its unit cannot be recovered afterwards.
Temperature is not a detail of this measurement, it is part of it. The conductivity of an aqueous solution rises roughly 2% per degree Celsius, so the same sample read at 20 °C and at 30 °C differs by around a fifth with no change in what is dissolved in it. Laboratory and process meters therefore report a temperature-compensated value normalised to 25 °C, and a figure from an uncompensated instrument is not comparable with one that has been corrected. Where two meters disagree, the compensation reference is the first thing to check.
Conductivity is routinely used as a stand-in for total dissolved solids, and the substitution is looser than it looks. Instruments derive TDS by multiplying conductivity by a factor typically between 0.5 and 0.7, chosen for an assumed mixture of salts — so the same water can be reported at noticeably different mg/L values by two meters that agree perfectly on conductivity. The underlying reason is that ions differ in how much current they carry: a solution dominated by sodium chloride and one dominated by calcium bicarbonate can share a conductivity without sharing a dissolved-solids figure.
Quick reference — 1 Microsiemens/centimeter (µS/cm) is equal to:
| Siemens/meter | S/m | 0.0001 |
| Millisiemens/meter | mS/m | 0.1 |
| Microsiemens/meter | µS/m | 100 |
| Siemens/centimeter | S/cm | 0.000001 |
| Millisiemens/centimeter | mS/cm | 0.001 |
| Megasiemens/meter | MS/m | 1.000000e-1 |
7 units of electric conductivity, each a fixed multiple of the S/m. The table spans 1,000,000,000,000:1, from µS/m (0.000001 S/m) to MS/m (1000000 S/m). Conversion is one multiplication into the base unit and one division out of it, with no lookup table and no approximation.
value_to = value_from × (factor_from ÷ factor_to)1 S/m = 1 S/m1 mS/m = 0.001 S/m1 µS/m = 0.000001 S/m1 S/cm = 100 S/m1 mS/cm = 0.1 S/m1 µS/cm = 0.0001 S/m1 MS/m = 1000000 S/mwhere:
Assumptions: Factors are exact definitions. Full double precision is carried internally and rounding is applied only for display.
Result25 µS/cm = 0.025 mS/cm
Conductivity is the reciprocal of resistivity, in siemens per metre (S/m). It is the standard way to describe how freely charge moves through a material, and outside the metals it is most often used for liquids.
Water quality is the everyday case. Ultrapure water is around 0.055 µS/cm, ordinary drinking water runs 50–800 µS/cm, and seawater is near 50,000 µS/cm — a span of roughly a million to one, which is why the microsiemens-per-centimetre scale exists at all rather than the SI S/m. A conductivity meter is really measuring dissolved ions, so the reading is used as a fast proxy for total dissolved solids rather than as an end in itself.