# mS/cm

> mS/cm (millisiemens per centimetre) is the standard unit of EC for nutrient solutions; 1 mS/cm equals 1 dS/m and 1,000 µS/cm.

- Canonical: https://genetixbay.com/knowledge/glossary/ms-cm.html
- Also written: millisiemens per centimetre, millisiemens per centimeter, mS, millisiemens, dS/m
- Glossary category: pH, EC and water · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

mS/cm (millisiemens per centimetre) is the unit used for [electrical conductivity](https://genetixbay.com/knowledge/glossary/ec.md) of nutrient solutions. The siemens is the unit of electrical conductance; dividing by the centimetre spacing of the probe gives conductivity. 1 mS/cm is numerically identical to 1 dS/m (decisiemens per metre), the unit preferred in soil science and irrigation papers.

## In practice

mS/cm is the unit to use when comparing numbers across meters, nutrient charts and research, because it is a real measurement, while ppm depends on which [conversion factor](https://genetixbay.com/knowledge/glossary/conversion-factor.md) your meter uses. A grower whose pen reads "1.6" in EC mode is at 1.6 mS/cm; the same solution might read 800 on a 500-scale [ppm meter](https://genetixbay.com/knowledge/glossary/ec-meter.md) or 1,120 on a 700-scale meter.

Some meters display EC without a unit, and some older ones read in mmho/cm, an old name for the same thing (1 mmho/cm = 1 mS/cm).

## Units and formula

| mS/cm | [µS/cm](https://genetixbay.com/knowledge/glossary/us-cm.md) | dS/m | [CF](https://genetixbay.com/knowledge/glossary/cf.md) | [ppm500](https://genetixbay.com/knowledge/glossary/ppm500.md) | [ppm700](https://genetixbay.com/knowledge/glossary/ppm700.md) |
|---|---|---|---|---|---|
| 1.0 | 1,000 | 1.0 | 10 | 500 | 700 |
| 1.5 | 1,500 | 1.5 | 15 | 750 | 1,050 |
| 2.0 | 2,000 | 2.0 | 20 | 1,000 | 1,400 |

## Don't confuse with

- **µS/cm**: a thousand times smaller unit, used for low-EC water.
- **ppm**: a calculated estimate, not a measured unit of conductivity.

## Related terms

[EC](https://genetixbay.com/knowledge/glossary/ec.md), [µS/cm](https://genetixbay.com/knowledge/glossary/us-cm.md), [CF](https://genetixbay.com/knowledge/glossary/cf.md), [ppm500](https://genetixbay.com/knowledge/glossary/ppm500.md), [ppm700](https://genetixbay.com/knowledge/glossary/ppm700.md)

## Read more

- [EC vs PPM: the 500 and 700 scales, CF, and how to convert](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md)

## Sources

1. University of California Cooperative Extension, Ventura County. Salinity units and conversions (640 ppm = 1 dS/m). https://ucanr.edu/node/125832
2. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test-water-quality