Anyone can clip a component into a fixture and read a value, yet two laboratories often disagree about the same part by several percent. Learning how to measure inductance with an LCR meter properly means understanding what the instrument actually does: it applies a small alternating signal, measures the voltage and current with their phase difference, and calculates an impedance that it then expresses through a chosen equivalent circuit.

Each of those steps involves a setting, and each setting can shift the answer. This guide covers the choices that matter, in the order you would make them at the bench, and then lists the usual causes of disagreement between supplier and customer readings. It follows the routine used at NG Electronics, an ISO 9001:2015 certified manufacturer in Pune, India, where LCR testers are used to check inductance on every unit produced.

What an LCR meter actually measures

The meter drives the component with a sine wave at a selected frequency and amplitude, then measures the magnitude and phase of the resulting impedance. From those two quantities it derives inductance together with a secondary parameter such as Q, dissipation factor or equivalent resistance. The inductance shown is therefore a calculated quantity that depends on the equivalent circuit selected, the frequency and the drive level, not a fixed property read directly.

It is also a small-signal measurement. The test current is typically a few milliamperes or less, so the core operates at a tiny flux density with no direct current bias. The reading corresponds to the initial inductance on a datasheet. It does not show how the part behaves at rated current, which requires a bias source or a pulse-based saturation test, both described in testing inductors and transformers.

Step-by-step: how to measure inductance with an LCR meter

First set the frequency. Use the value on the datasheet; common choices are 1 kHz for large inductances, 10 kHz for mains filter chokes and 100 kHz for small power inductors. If nothing is stated, pick a frequency at which the reactance is conveniently between a few ohms and a few kilohms, and well below the self-resonant frequency. Next set the signal level, again following the datasheet, because high-permeability ferrite cores change inductance noticeably with drive level.

Then compensate the fixture, connect the part and read the value once the display settles. Record frequency, level and model alongside the result so the measurement can be repeated. Before fitting parts to a board, comparing the reading with an estimate from the inductance calculator is a quick sanity check on turns count and core material. Keep the component away from steel bench surfaces and other magnetic objects, which can disturb open-core parts.

• Select frequency and signal level to match the specification.
• Choose the series or parallel equivalent circuit.
• Perform open and short compensation with the actual fixture.
• Connect with four-terminal Kelvin contacts and take the reading.
• Record all conditions with the result.

Series or parallel model: Ls versus Lp

The meter can represent the part as an inductance in series with a resistance, giving Ls, or in parallel with a resistance, giving Lp. For a low-loss component the two values are almost identical. They diverge as Q falls, because the same measured impedance is being split in two different ways. A reading taken in the wrong mode on a lossy part can differ from the specification by more than the tolerance.

As a general rule, use the series model when the impedance is low, typically below about 100 Ω, since winding resistance is then the significant loss. Use the parallel model when the impedance is high, typically above about 10 kΩ, since core loss and stray capacitance act in parallel. Between those values either may be used, provided both parties use the same one. Most power inductors and chokes are specified in series mode.

Fixtures, compensation and lead effects

Test leads have their own inductance, resistance and capacitance. Open compensation measures the stray admittance of the fixture with nothing connected, and short compensation measures its residual impedance with the contacts joined by a low-inductance link. The meter then subtracts both. Without this step, a few centimetres of lead can add tens of nanohenries, which is a large error on a 1 µH part and negligible on a 10 mH choke.

Four-terminal Kelvin connections separate the current-carrying contacts from the voltage-sensing ones, removing contact resistance from the result, which matters for low-value inductors and for DCR. Keep the lead geometry unchanged after compensation, since moving the cables alters their inductance. For leaded parts such as toroidal power inductors, measure at a consistent point on the leads, and make sure enamel is fully removed where the contacts touch.

Why readings disagree and how to resolve it

Most disputes trace back to a handful of causes: different test frequency, different signal level, series against parallel mode, missing compensation, or temperature. Ferrite permeability changes with temperature, so a part measured in a cold stores area may differ from the same part at 25 °C. Measuring too close to self-resonance inflates the apparent inductance, as explained in inductor Q factor and self-resonant frequency. Agreeing a written test condition on the drawing removes nearly all of these.

Multi-winding parts need extra care. Leakage inductance is measured on one winding with the others shorted, and common mode chokes are measured on one winding with the other open; details appear in transformer testing and design validation. NG Electronics supplies a test certificate with orders on request and documents its checks on the quality assurance page. Buyers evaluating an inductor manufacturer in Pune, a choke coil manufacturer in India or any OEM inductor manufacturer should ask for the test conditions behind each reported value.

Frequently asked questions