Most standard digital multimeters cannot measure inductance directly. They lack the internal oscillator needed to test how an inductor behaves with alternating current, which is fundamental to measuring inductance. If your multimeter has a dedicated inductance mode (marked “L” or “H” on the dial), you can use it for rough measurements, but the results will be less accurate than a dedicated tool. For precise work, you need either an LCR meter or an indirect measurement method using equipment you may already have on your bench.
Why Standard Multimeters Fall Short
Inductance is an AC property. It describes how a coil resists changes in current flow, and that behavior depends on frequency. A standard multimeter works with DC quantities, so it has no way to apply an AC test signal and observe the inductor’s response. When budget multimeters do include an inductance function, they typically use a fixed low-frequency signal that ignores important characteristics like the coil’s internal resistance and how it performs at the frequency your actual circuit operates at.
An LCR meter solves this problem with a built-in oscillator that produces a small AC signal across a range of frequencies, commonly 100 Hz, 1 kHz, 10 kHz, and up to 100 kHz on higher-end models. This lets you test the inductor at a frequency close to what it will experience in your circuit. LCR meters also measure quality factor (Q) and dissipation factor (D), which tell you how much energy the inductor wastes as heat. Handheld LCR meters are available for $30 to $150 and offer basic accuracy around ±0.05% at their best measurement ranges.
What You Can Measure With a Multimeter
Your multimeter is still useful for one critical inductor test: DC resistance, often called DCR. Set your meter to resistance mode, place the probes across the inductor’s leads, and read the value. This tells you the resistance of the wire winding itself. A good inductor should show a relatively low resistance (often under a few ohms for power inductors), and an open-circuit reading means the winding is broken. A short to ground or an unexpectedly low reading can indicate shorted turns.
DCR matters because that winding resistance contributes to energy loss in your circuit. It also affects the accuracy of indirect inductance measurements, since the resistance is in series with the inductance and needs to be accounted for.
The Voltage-and-Frequency Method
If you have a signal generator (or a function generator app and an audio amplifier), you can measure inductance indirectly using your multimeter set to AC voltage mode. This approach treats the inductor as part of a simple voltage divider and uses Ohm’s law for AC circuits.
- Step 1: Connect a known resistor in series with the inductor. Choose a resistor value roughly in the range you expect the inductor’s impedance to be (100 ohms is a reasonable starting point for many small inductors).
- Step 2: Apply a sine wave from your signal generator at a known frequency. Something between 1 kHz and 10 kHz works well for most inductors.
- Step 3: Use your multimeter in AC voltage mode to measure the voltage across the resistor, then across the inductor.
- Step 4: Calculate the inductor’s impedance using the ratio of voltages. The inductive reactance (XL) equals 2π × frequency × inductance.
Rearranging that formula: L = XL / (2π × f). So if you determine the inductor has a reactance of 628 ohms at 1 kHz, the inductance is 628 / (2 × 3.14159 × 1000) = 0.1 H, or 100 mH. This method is approximate because your multimeter’s AC voltage reading may not be perfectly accurate at higher frequencies, but it gets you in the right ballpark.
The Resonant Frequency Method
This is the most accurate indirect method available without an LCR meter. You pair your unknown inductor with a known capacitor to create an LC circuit, then find the frequency where the circuit resonates. At resonance, you can calculate inductance using the formula:
L = 1 / (4π² × f² × C)
Here, f is the resonant frequency in hertz and C is the capacitance in farads. To do this, connect the inductor and a known capacitor in parallel, feed in a sine wave from a signal generator, and sweep the frequency while monitoring the output voltage with your multimeter (AC mode) or an oscilloscope. The resonant frequency is the point where the voltage peaks.
For example, if you use a 100 nF capacitor and find resonance at 5,000 Hz, the inductance works out to about 10.1 mH. The accuracy depends heavily on how precisely you know your capacitor’s value and how accurately you can identify the peak frequency. Using a capacitor with a tight tolerance (5% or better) and sweeping the frequency slowly near the peak will give the best results.
The Time Constant Method
If you have an oscilloscope alongside your multimeter, you can measure inductance through the RL time constant. When you suddenly apply a voltage to a resistor and inductor in series, the current doesn’t jump instantly to its maximum. Instead, it rises gradually and reaches about 63.2% of its final value after one time constant.
The time constant (τ) for an RL circuit equals L / R. If you know R (your series resistor) and can measure τ on the oscilloscope, then L = τ × R. Apply a square wave to the RL series circuit and observe the exponential rise on the oscilloscope. Measure the time it takes for the voltage across the resistor to reach 63.2% of its maximum. Multiply that time by the resistance, and you have your inductance.
This method works best for larger inductors (millihenry range and above), where the time constant is long enough to see clearly on a basic oscilloscope. For tiny inductors in the microhenry range, the time constant may be nanoseconds, which requires faster equipment.
Understanding Inductance Units
Meter displays and component markings use several different units, and mixing them up is an easy mistake. The base unit is the henry (H), but most real components are much smaller:
- 1 henry (H) = 1,000 millihenries (mH)
- 1 millihenry (mH) = 1,000 microhenries (µH)
- 1 microhenry (µH) = 1,000 nanohenries (nH)
Small power inductors and RF chokes are typically in the microhenry range (1 to 1,000 µH). Audio crossover inductors and filter coils often fall in the millihenry range. Full henries are rare outside of large iron-core transformers and specialty applications. When your meter displays “0.47 mH,” that’s the same as 470 µH.
Common Sources of Error
Several factors can throw off your inductance readings regardless of which method you use. Lead resistance is one: the resistance of your test leads adds to the inductor’s own winding resistance, which can distort results in low-impedance measurements. Use short leads and subtract their resistance if necessary.
Core saturation is a bigger concern for inductors with ferrite or iron cores. At low test currents (the kind a meter or LCR meter applies), the core behaves normally. But in a real circuit carrying significant DC current, the core can saturate, causing the effective inductance to drop by 80% or more. This means a component that measures 100 µH on your bench might act like 20 µH in your circuit. If you’re troubleshooting a circuit where an inductor isn’t performing as expected, saturation under load is a likely culprit that bench measurements won’t reveal.
Stray capacitance from nearby components or long test leads can also affect readings, especially at higher frequencies. Keep the inductor isolated from other components during testing, and avoid coiling your test leads (which adds their own small inductance to the measurement).
Safety With Large Inductors
Inductors store energy in their magnetic fields, and that energy has to go somewhere when the circuit is interrupted. When you disconnect a large energized inductor, the collapsing magnetic field converts back into electrical energy, producing a high-voltage spike at the break point. This flyback voltage can cause painful shocks, damage your meter, or create destructive arcing.
Before measuring any inductor, verify it is fully de-energized and disconnected from its circuit. If the inductor was recently powered, give it a moment and check for residual voltage with your multimeter before touching the leads. This is primarily a concern with large inductors in power supplies, motor drives, and energy storage applications, not with the small surface-mount components on a PCB.