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TDS to Conductivity Calculator

Convert total dissolved solids (ppm) to electrical conductivity in µS/cm and mS/cm using a selectable conversion factor.

Total dissolved solids

TDS factor

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How it works

EC (µS/cm) = TDS (ppm) ÷ factor · mS/cm = µS/cm ÷ 1000

Dissolved ions carry current, so total dissolved solids and electrical conductivity track each other, related by an empirical factor between about 0.5 and 0.7. Meters measure conductivity directly and multiply by the factor to display TDS, so to recover conductivity from a TDS reading you divide by the same factor. The right factor depends on which salts dominate — 0.5 suits sodium-chloride-like waters, 0.7 potassium chloride standards, and 0.64 is a common all-purpose value.

Worked example

A reading of 500 ppm TDS with the 0.64 factor implies 500 ÷ 0.64 = 781 µS/cm, or 0.781 mS/cm. Switching to the 0.5 NaCl factor would instead give 1,000 µS/cm from the same dissolved-solids figure.

Frequently asked questions

Why do two meters disagree on TDS?

They almost always use different conversion factors. A meter on the 0.5 NaCl scale reports a lower TDS than one on 0.7 for the same water. Compare the raw conductivity in µS/cm instead — that is the actual measured quantity.

Which factor should I pick?

For general tap or aquarium water 0.64 is a safe default. Use 0.5 when sodium chloride dominates and 0.7 for hydroponics nutrient solutions calibrated to KCl. When in doubt, report conductivity rather than TDS.

What conductivity is pure water?

Truly pure deionised water is around 0.055 µS/cm; typical RO water is a few µS/cm, tap water 100–800 µS/cm, and seawater about 50,000 µS/cm. TDS scales roughly in proportion.

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This calculator is for educational purposes. Double-check important results before acting on them.