ohmcm

Ohmcm is not a formal unit or widely recognized term in standard references; it is most often encountered as a concatenation of “ohm” and “cm” in informal text. In many contexts, ohmcm is used to refer to the unit ohm-centimeter, symbolized as Ω·cm, which is the CGS (centimeter-gram-second) unit of electrical resistivity.

Ohm-centimeter measures a material’s intrinsic resistance to electrical current per cross-sectional area. Resistivity ρ is defined by ρ = R·A/L, where R is resistance, A is cross-sectional area, and L is length. When ρ is expressed in Ω·cm, a cube measuring 1 cm on each side would have a resistance of 1 Ω between opposite faces. The relation to the SI unit is 1 Ω·cm = 0.01 Ω·m; conversely, 1 Ω·m = 100 Ω·cm. This unit is commonly used for liquids, polymers, doped semiconductors, and other materials where CGS reporting is standard or convenient.

Usage and notes: the correct formal notation is Ω·cm or Ω cm; the concatenated form ohmcm is informal and can lead to ambiguity. Values of resistivity span many orders of magnitude, from very high (insulators) to very low (good conductors). For example, ultra-pure water has resistivity around 18.2 MΩ·cm, while typical copper metal has a resistivity on the order of 1.68×10^-6 Ω·cm at room temperature.

See also: electrical resistivity, ohm-meter, ohm-centimeter, material properties.