Water quality · TDS

TDS and conductivity converter.

Turn a conductivity reading into an estimated TDS, or the reverse, with a factor you can change.

µS/cm and mS/cmEditable factor500 mg/L objective

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Inputs

Common rule of thumb is roughly 0.5 to 0.7, not a published standard. It depends on which ions are in the water; calibrate with a lab TDS if you need accuracy.

Result

Enter your numbers.

TDS and Conductivity Converter (ppm, µS/cm): how it works

TDS in mg/L is roughly conductivity in µS/cm times a factor, often given as about 0.5 to 0.7 (a common rule of thumb, not from the sources below). This tool uses a factor you set (default 0.65). Health Canada notes that conductivity can serve as a surrogate for TDS, but that the method should only be used if a calibration curve has been established for the specific water type, so treat the result as an estimate.

Worked example. A meter reads 800 µS/cm. With a factor of 0.65, TDS is 800 x 0.65 = 520 mg/L, which is above the 500 mg/L aesthetic objective. In reverse, 300 ppm TDS divided by 0.65 is about 462 µS/cm (0.462 mS/cm).

The 500 mg/L figure. Both Health Canada (aesthetic objective, 500 mg/L or less) and the US EPA (secondary standard, 500 mg/L) use 500 mg/L for TDS. It is based on taste and scaling, not toxicity. EPA lists hardness, deposits, colored water, staining and salty taste as the issues.

Frequently asked questions

What is the conversion factor from µS/cm to ppm?

There is no single factor. A common rule of thumb, not from the sources listed on this page, is about 0.5 to 0.7. This tool defaults to 0.65 and lets you change it.

Is 1 mS/cm the same as 1,000 µS/cm?

Yes. 1 mS/cm is 1,000 µS/cm.

What TDS is too high for drinking water?

Health Canada and the US EPA both give 500 mg/L as a taste-based objective. It is not a health-based limit.

Why can a conductivity estimate differ from a lab TDS?

Health Canada says conductivity should only be used as a TDS surrogate if a calibration curve has been established for the specific water type. A single factor is only an estimate.

Sources

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Runs entirely in your browser. Nothing you type is sent or stored.

Not professional advice

Estimates only. A conductivity-based TDS is not a lab result and says nothing about specific contaminants. Not professional advice.

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