Ohm (Ω)
The ohm defined, the standard resistor value series, why E12 values look so arbitrary, and the resistance scale from milliohms to gigaohms.
Questions people ask
Why are resistor values like 4.7 kΩ and 6.8 kΩ?
They come from the E12 series, spaced logarithmically so that consecutive ± 10% ranges just meet. Any target value is then within tolerance of a stock part.
What is impedance measured in?
Also ohms. Impedance is the AC generalisation of resistance, adding the frequency-dependent contributions of capacitance and inductance.
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Last updated 22 August 2026