circular mil ohm/foot Unit Converter

Definition of circular mil ohm/foot unit

Circular mil ohm per foot (Ω·cmil/ft) is a resistivity unit expressing the resistance, in ohms, of a material one foot long with a cross-sectional area of one circular mil. One unit equals approximately 1.662 × 10⁻⁹ Ω·m.

History of circular mil ohm/foot unit

The unit emerged from the practical engineering system built around the inch, mil, and foot, especially in North American wire manufacturing and electrical design. A circular mil defines a wire’s area from its diameter in thousandths of an inch, simplifying calculations for round conductors. Engineers paired this area with ohmic resistance and length to produce the ohm-circular-mil-per-foot resistivity convention. Tables popularized values for copper, aluminum, and alloys before metric SI units became dominant. It remains a legacy US customary unit in wire charts, handbooks, and older standards.

Applications of circular mil ohm/foot unit

Today, circular mil ohm per foot is used mainly in North American electrical engineering, cable specifications, and educational references. Designers use tabulated resistivities to calculate voltage drop, conductor resistance, heating, and required wire size. Typical approximate values are 10.4 for copper, 17 for aluminum, and higher values for resistance alloys. Modern software often converts the unit to Ω·m.

Complete list of circular mil ohm/foot unit conversion