Electric Resistivity converter

The ohm meter (Ω·m) is the reference unit for electric resistivity, describing how strongly a material resists current flow independent of its shape. The other units scale down from it: an ohm centimeter (Ω·cm) is 0.01 Ω·m, an ohm inch (Ω·in) is 0.0254 Ω·m, a microohm meter (µΩ·m) is a millionth of an ohm meter, a microohm centimeter (µΩ·cm) is 1e-8 Ω·m, and a nanoohm meter (nΩ·m) is a billionth of an ohm meter. The abohm centimeter (abΩ·cm), from the old CGS system, is an extremely small 1e-11 Ω·m, while the ohm circular-mil per foot (Ω·cmil/ft) — a unit unique to American wire tables — equals about 1.662426113e-9 Ω·m.

The featured pair here converts microohm centimeter to ohm meter with Ω·m = µΩ·cm × 1e-8, and the reverse direction multiplies by 100,000,000.

Copper's resistivity is commonly quoted as about 1.68 µΩ·cm at room temperature; applying the formula gives 1.68 × 1e-8 = 1.68e-8 Ω·m, the figure most materials tables use. Converting an ohm meter down to ohm centimeters is simpler still: a resistivity of 2 Ω·m becomes 2 ÷ 0.01 = 200 Ω·cm, since one ohm centimeter is a hundredth of an ohm meter.

Resistivity is the property engineers actually care about when choosing a conductor, because it describes the material itself rather than a particular wire's size. Cable and busbar designers use Ω·m or µ·Ω·cm figures to compare copper, aluminum, and exotic alloys before settling on a cross-section for a given current rating, and semiconductor fabrication relies on resistivity measured in Ω·cm to characterize how heavily a silicon wafer has been doped — lower resistivity generally means more dopant atoms per volume.

The American wire industry's ohm circular-mil per foot deserves special mention: copper's resistivity in that unit is often tabulated as roughly 10.4 Ω·cmil/ft, a number that looks completely unrelated to the familiar 1.68 µΩ·cm figure, even though both describe the same metal. The mismatch isn't an error — circular-mil-per-foot bakes in a different, non-metric way of describing a wire's cross-sectional area (the circular mil), so the raw numbers simply live on different scales until you run the conversion.

Resistivity should also not be confused with resistance itself, even though the two units look similar. Resistance (in ohms, covered on its own page) depends on a specific object's length and cross-section as well as its material, while resistivity is the material property alone, with length and area already normalized out. Doubling a wire's length doubles its resistance but leaves the wire's resistivity completely unchanged, since resistivity describes copper or aluminum as a substance, not any particular piece of it.

Temperature matters here too: a material's resistivity figure is only meaningful alongside the temperature it was measured at, since resistivity for most metals rises with heat. The commonly cited 1.68 µΩ·cm for copper is specifically a room-temperature figure (around 20°C); the same copper sample measured on a hot summer day inside a running motor winding will show a noticeably higher resistivity, which engineers account for when predicting how much a winding's resistance — and its heat losses — will grow as it warms up under load.