Conductivity Converter
Convert siemens per metre, mS/cm, microsiemens and %IACS — the water-quality and metallurgy scales side by side, with the TDS factor treated as the estimate it actually is.
Conductivity Converter
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What this result does not account for
- Water-quality bands are typical ranges for orientation and are not regulatory limits, which differ by jurisdiction and by intended use.
- The TDS estimate is empirical and instrument-dependent; it is not a unit conversion and should not be reported as a measured value.
- Solution conductivity varies strongly with temperature. This converter does not apply temperature compensation, and assumes any value you enter has already been compensated to 25 °C if that matters to your application.
In short: Electrical conductivity converts through the siemens per metre. Two everyday scales sit on top of it: water laboratories work in µS/cm and mS/cm, while metallurgy uses %IACS, a ratio against annealed copper fixed at 58.0 MS/m. Note that dS/m and mS/cm are the same magnitude under two names, and that converting conductivity to TDS in ppm is an estimate, not a unit conversion.
Formula
Each factor is the number of siemens per metre in one of that unit. The siemens is the reciprocal ohm, once called the mho. The %IACS factor is 580,000 S/m per percent, one hundredth of the 58.0 MS/m copper reference.
Worked Example
- Identify the source factor. One µS/cm is 0.0001 S/m.
- Convert to the SI unit. 1,000 × 0.0001 = 0.1 S/m.
- Identify the target factor. One S/m is 1.
- Divide. 0.1 ÷ 1 = 0.1 S/m, which is also 1 mS/cm and 1 dS/m — the same number under three names.
- Keep TDS separate. That same water reads 500 ppm on a NaCl-calibrated meter and 700 ppm on a 442 meter.
Why dS/m and mS/cm are identical. A decisiemens is a tenth of a siemens, so dS/m is 0.1 S/m. A millisiemens is a thousandth of a siemens and a centimetre is a hundredth of a metre, so mS/cm is 0.001 ÷ 0.01 = 0.1 S/m as well. Soil scientists write dS/m and water chemists write mS/cm out of convention alone. Listing both as separate rows would imply a conversion exists between them, so this converter shows one row carrying both names.
Strengths & Limits Of This Model
Where this engine is strong
- Collapses dS/m and mS/cm into one honest row instead of implying a conversion exists between identical magnitudes.
- Carries the %IACS metallurgy scale alongside the water-quality scales, which most converters separate.
- Shows resistivity alongside conductivity so the reciprocal is always visible.
Where it stops
- Does not perform temperature compensation.
- The TDS card cannot be more precise than the calibration salt allows.
- Does not calculate the resistance of a specific conductor, which needs length and cross-section.
Practical Use Cases
Water quality and treatment
Conductivity is the fastest proxy for dissolved ion load. Reverse osmosis performance, boiler feedwater limits and aquarium chemistry are all specified in µS/cm or mS/cm.
Agriculture and hydroponics
Soil and nutrient solution salinity are quoted in dS/m, which is the same number as mS/cm. Crop tolerance thresholds are published on this scale.
Metallurgy and conductor selection
Copper alloys, aluminium grades and contact materials are specified in %IACS. Converting to MS/m makes them directly comparable with resistivity data.
Cable and busbar engineering
Conductor conductivity feeds directly into resistance and voltage drop through R = ρL/A — see the Resistance Converter for the object-level side of that relationship.
Methodology & Editorial Standards
All conversions route through the siemens per metre, the SI unit of electrical conductivity and the exact reciprocal of the ohm-metre. The siemens was formerly called the mho and the two are the same unit, so they share a row. Likewise the decisiemens per metre and the millisiemens per centimetre are both exactly 0.1 S/m and appear as a single entry, because presenting them separately would falsely imply a conversion between them. The %IACS scale is referenced to the International Annealed Copper Standard of 1913, which fixes annealed copper at 58.0 MS/m at 20 °C, equivalent to a resistivity of 1.7241 µΩ·cm; because that scale is a simple ratio it is linear and can be treated as a unit. Total dissolved solids is deliberately NOT offered as a unit: the relationship between conductivity and TDS is empirical, depends on which ions are present, and the industry-standard factors span 0.50 to 0.70, so it is presented as a clearly labelled estimate carrying its own assumption. Conductivity is also strongly temperature-dependent in solution, and readings are conventionally compensated to 25 °C. All conversion factors are exact by definition under the International System of Units, or exact by international agreement where the unit is defined by treaty. Values are held at full IEEE-754 double precision internally and rounded only for display, so chained conversions do not accumulate drift.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Conductivity Converter — 9 Expert FAQs
9 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
Is dS/m the same as mS/cm?
Yes, exactly. A decisiemens per metre is 0.1 S/m and a millisiemens per centimetre is 0.001 divided by 0.01, which is also 0.1 S/m. They are one magnitude under two names, kept alive by convention: soil science and irrigation use dS/m while water chemistry and aquaculture use mS/cm. If a converter lists them as separate rows with a factor of 1 between them, it is padding its unit list.
How do I convert conductivity to TDS in ppm?
Multiply the reading in µS/cm by a factor between 0.5 and 0.7, but understand that this is an estimate rather than a conversion. The factor depends on which ions are dissolved and on which salt your meter was calibrated against: 0.5 for NaCl, around 0.55 for KCl, and 0.65 to 0.85 for the 442 natural-water blend. The same sample can legitimately read 500 or 700 ppm on two correctly working meters.
What does %IACS mean?
Percent of the International Annealed Copper Standard, adopted in 1913. It fixes commercially pure annealed copper at 58.0 MS/m at 20 °C and expresses every other material as a percentage of that. Aluminium is roughly 61%, brass 25 to 37%, and modern refined copper cathode often exceeds 100% because it is purer than the 1913 reference sample.
What is the difference between conductivity and conductance?
Conductivity is a property of a material, measured in siemens per metre. Conductance is a property of a specific object, measured in siemens, and depends on that object's length and cross-section as well as its material. The same distinction separates resistivity from resistance. This page converts conductivity; the resistance converter handles the object.
Is a mho the same as a siemens?
Yes. The mho is the older name, being ohm spelled backwards, and it was formally replaced by the siemens in 1971. They are numerically identical, which is why they share a single row here. You will still encounter mho/cm and micromho/cm in older American literature and on legacy instruments.
Why does temperature matter so much for water conductivity?
Ion mobility rises with temperature, so the same water reads higher when warmer, typically by around 2% per degree Celsius. Laboratory and field instruments therefore compensate readings to a reference of 25 °C. Comparing an uncompensated summer field reading with a compensated laboratory result can produce a difference of ten per cent or more with no change in the water at all.
What conductivity should drinking water have?
Most potable supplies fall somewhere between 50 and 1,500 µS/cm. Very low readings indicate water so pure it has little mineral content, while high readings indicate heavy dissolved load. Conductivity says nothing about what the ions are, so it cannot detect contamination by non-conductive substances and is a screening measure rather than a safety test.
Can conductivity be negative?
No. It is bounded below by zero, which corresponds to a perfect insulator. A negative reading on an instrument indicates a calibration fault, a polarity error or a damaged probe. This converter refuses negative input rather than returning a tidy but meaningless negative result.
How does conductivity relate to resistance in a cable?
Through R = ρL/A, where ρ is resistivity, the reciprocal of conductivity. Copper at 58 MS/m has a resistivity of about 1.724 µΩ·cm, so 100 metres of 2.5 mm² copper works out to roughly 0.69 ohms. Conductivity alone tells you nothing about a cable until you supply its length and cross-section.