Electric Conductance converter

The siemens (S) is the reference unit for electric conductance, the reciprocal of resistance, and the other units scale it in the usual decimal steps: a kilosiemens (kS) is 1,000 S, a millisiemens (mS) is 0.001 S, and a microsiemens (µS) is a millionth of a siemens. The mho (℧) — literally "ohm" spelled backward — is the older name for the same unit and equals exactly 1 S, with micromho (µ℧) equal to 1e-6 S just like microsiemens. The CGS-derived abmho is a large 1,000,000,000 S, while the statmho is a tiny 1.112650056e-12 S. The ampere per volt (A/V) is Ohm's law inverted into a unit name, and it too equals exactly 1 S.

The page's featured pair converts millisiemens to siemens using S = mS × 0.001, with the reverse direction multiplying by 1,000.

A sensor with a conductance of 350 mS converts to 350 × 0.001 = 0.35 S. A water-quality probe reading 80 µS converts up to 0.08 mS, and since siemens and mho are numerically identical, a conductance of 2 S can be written equally correctly as 2 mho with no multiplication at all.

Conductance is the natural quantity to reach for whenever a circuit element's ability to pass current, rather than resist it, is the point of interest — switches, relay contacts, and fuses are often rated by how much conductance they maintain when closed. It also shows up heavily in chemistry and water testing, where the electrical conductance of a solution (closely related to conductivity, covered on its own page here) indicates how many dissolved ions are present, which is why lab conductance meters report readings in siemens or millisiemens.

The main point of confusion is the naming overlap between "mho" and "siemens": they are the same unit, not a conversion pair, so a device spec sheet written decades apart might use either symbol for an identical value. It's also easy to mix up conductance (siemens, S) with conductivity (siemens per meter, S/m, covered on a separate page), since conductance describes a specific component or sample while conductivity describes the material property independent of its shape.

It's worth remembering, too, that conductance is not simply "the opposite" of resistance in every practical sense, even though mathematically G = 1/R. A component's resistance can change with temperature, frequency, or applied voltage, and its conductance changes right along with it in the inverse direction, so a single conductance figure is only as meaningful as the conditions under which it was measured — the same caution that applies to any resistance rating applies here too, just flipped upside down.

Conductance figures are also useful for combining parallel paths without extra arithmetic gymnastics: whereas resistors in parallel need a reciprocal-of-sums formula, conductances in parallel simply add together directly, since two paths sharing a voltage pass a combined current equal to the sum of what each path would pass alone. Engineers sketching out a parallel network sometimes switch to conductance purely for that bookkeeping convenience before converting back to ohms for the final answer.