Electric Resistance Converter

Electric resistance is the property of a material that opposes the flow of electric current. It is one of the three fundamental quantities in Ohm's law (V = IR), alongside voltage and current, and determines how much current flows through a circuit for a given applied voltage. From the 0.1-milliohm resistance of a high-quality switch contact to the teraohm resistance of a glass insulator, electric resistance spans more than 15 orders of magnitude in engineering practice. This converter supports ten units covering SI, CGS-EMU, CGS-ESU, and quantum standards.

The SI unit of resistance is the ohm (Ω), named after German physicist Georg Simon Ohm. One ohm is defined as the resistance that allows exactly one ampere of current to flow when one volt of potential difference is applied. Resistors — the components that implement resistance in circuits — range from a few milliohms in power electronics shunts to teraohms in instrumentation amplifier inputs. The ohm is also equivalent to one reciprocal siemens (1 Ω = 1/S), connecting resistance to its inverse quantity, conductance.

For large resistance values, the megohm (MΩ) is the practical unit. Insulation resistance testers (meggers) measure the resistance of cable insulation, motor windings, and transformer coil insulation in megohms. A new cable should exhibit insulation resistance of hundreds of megohms to gigaohms. As insulation deteriorates due to moisture, heat, or mechanical damage, this value drops, providing an early warning of impending failure.

At the small end, the microhm (µΩ) is used for contact resistance, weld joint resistance, busbar connection resistance, and PCB via resistance. In high-current applications like battery interconnects and motor windings, even microohm-level contact resistance can cause significant heat generation when hundreds or thousands of amperes flow through. Four-wire (Kelvin) resistance measurement is used at this scale to eliminate lead resistance errors.

The abohm — the CGS electromagnetic unit of resistance — equals exactly 10⁻⁹ ohms (one nanoohm), making it astronomically small by SI standards. One ohm equals one billion abohms. The CGS-EMU system built resistance from the fundamental quantities of length, mass, and time, resulting in units poorly matched to practical electrical measurements. The abohm and its kin were replaced by SI units for virtually all engineering purposes after 1960.

The statohm — the CGS electrostatic unit of resistance — goes to the opposite extreme: 1 statohm ≈ 8.9876 × 10¹¹ ohms (nearly 900 gigaohms). This enormous value reflects the fact that the statcoulomb (CGS-ESU charge unit) is much smaller than the coulomb, requiring huge resistance values to produce sensible current flow. The statohm appears in classical electrostatics and some plasma physics texts.

The Quantized Hall Resistance is unique among resistance units — it is a fundamental physical constant, the von Klitzing constant R_K = h/e² ≈ 25,812.807 Ω. It arises in the integer quantum Hall effect, observed in two-dimensional electron gases cooled to millikelvin temperatures in strong magnetic fields. Its exact value makes it the basis of the international resistance standard since 1990, providing a reproducible, artifact-free resistance reference used by national metrology institutes worldwide.

This tool supports all ten electric resistance units: ohm, megohm, microhm, volt/ampere [V/A], reciprocal siemens [1/S], abohm, EMU of resistance, statohm, ESU of resistance, and Quantized Hall resistance. Whether you need to convert legacy CGS literature values, check insulation ratings in megohms, or work with nanoscale resistance measurements in microohms, Unit Converters Lab provides instant, precise conversions with no downloads or account required.