Electric Resistivity Converter

Electric resistivity, symbolised by the Greek letter rho (ρ), is an intrinsic material property that quantifies how strongly a substance resists the conduction of electric current. Unlike resistance, which depends on an object's geometry, resistivity is purely a material property — it remains the same regardless of the size or shape of the sample. This makes resistivity the universal benchmark for comparing the electrical properties of metals, semiconductors, insulators, and liquids across research and industry.

The SI unit of electric resistivity is the ohm meter (Ω·m). The resistance R of any conductor made from a material with resistivity ρ can be calculated as R = ρL/A, where L is the conductor's length and A is its cross-sectional area. This relation is fundamental to wire sizing calculations, PCB trace resistance estimation, and the design of precision resistors. Resistivity values span an enormous range: from about 1.59 × 10⁻⁸ Ω·m for silver (the best metallic conductor) to more than 10¹⁶ Ω·m for fused quartz (an excellent insulator).

For metals and semiconductor materials, the ohm centimeter (Ω·cm) is widely used. Silicon's intrinsic resistivity at room temperature is approximately 640 Ω·cm, while doped silicon used in transistors ranges from 10⁻³ to 10³ Ω·cm depending on dopant concentration. The germanium used in early transistors has a resistivity of about 47 Ω·cm. Converting between Ω·cm and Ω·m is simple: divide by 100 to go from Ω·cm to Ω·m.

For precise metallic resistivity measurements, the microhm centimeter (µΩ·cm) is the most practical unit. Since 1 µΩ·cm = 10⁻⁸ Ω·m, the resistivity of copper (1.68 × 10⁻⁸ Ω·m) is simply written as 1.68 µΩ·cm. This unit is standard in metallurgy, thin-film deposition monitoring, and electroplated copper quality assessment. Aluminium is 2.82 µΩ·cm, gold is 2.44 µΩ·cm, and stainless steel ranges from 69 to 72 µΩ·cm.

In North American wire and cable engineering, the circular mil ohm per foot (cmil·Ω/ft) is the preferred unit for resistivity, directly matching the NEC wire table format where conductor cross-sections are given in circular mils and lengths in feet. The resistivity of standard annealed copper is 10.37 cmil·Ω/ft at 20°C, and this value is used to calculate the resistance of any copper conductor when its circular mil area and length in feet are known.

The ohm inch (Ω·in) appears in some American engineering standards, particularly in specifications for resistive heating elements and thermistors where dimensions are naturally measured in inches. The conversion is 1 Ω·in = 0.0254 Ω·m. The microhm inch (µΩ·in) is similarly used for metallic material resistivity in inch-based manufacturing specifications.

CGS units complete the picture: the abohm centimeter (abΩ·cm) equals 10⁻¹¹ Ω·m in the EMU system, while the statohm centimeter (stΩ·cm) equals approximately 8.9876 × 10⁹ Ω·m in the ESU system. These units appear in pre-SI electromagnetic literature and provide historical context for the development of modern electrical measurements.

This converter supports all eight resistivity units: ohm meter, ohm centimeter, ohm inch, microhm centimeter, microhm inch, abohm centimeter, statohm centimeter, and circular mil ohm/foot. Whether you are reading materials datasheets, designing wire harnesses, or translating CGS literature to SI, Unit Converters Lab provides accurate, instant conversions with no login or installation required.