Calculate inductive reactance, inductance, or frequency using the inductive reactance formula (XL = 2πfL).
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Inductive reactance (denoted XL) is the opposition an inductor presents to a changing alternating current passing through it, and it's calculated from the relationship XL = 2π × f × L, where f is the AC frequency in hertz and L is the inductor's inductance in henries. Inductive reactance increases as frequency or inductance rises, unlike the capacitive reactance of capacitors, which decreases as frequency rises — an important and frequently tested contrast in circuit analysis, since it means inductors and capacitors respond in exactly opposite ways to changing signal frequency. This calculator lets you find any one of the three quantities (reactance, inductance, or frequency) if the other two are known, and it's useful in designing filter circuits and resonant circuits that rely on the interaction between capacitors and inductors, such as radio tuning circuits and power supply filters that must pass or block specific frequency ranges.
Inductors and capacitors are often introduced together in circuit theory because they share a kind of mirror-image relationship: whatever an inductor does as frequency changes, a capacitor does the opposite, and this opposing behavior is exactly what makes filter and resonant circuits possible.
An inductor resists changes in current through a physical mechanism rooted in electromagnetic induction — as current tries to change, the inductor's magnetic field change generates a voltage that opposes that change. Faster-changing current (higher frequency) triggers a stronger opposing effect, which is why inductive reactance increases with frequency: at high frequencies, an inductor increasingly blocks current flow, while at low frequencies (approaching DC), it offers little resistance at all.
A capacitor works by the opposite underlying mechanism, storing charge on its plates in response to voltage. At low frequencies, a capacitor has plenty of time to fully charge and discharge each cycle, presenting significant opposition to current flow. At high frequencies, the capacitor doesn't have time to fully charge before the voltage reverses, so it presents progressively less opposition — hence capacitive reactance decreases as frequency rises, precisely the opposite pattern from an inductor.
This opposing frequency behavior is what makes it possible to build filters that selectively pass or block certain frequencies: a simple low-pass filter can use a capacitor to short high frequencies to ground while passing low frequencies through, and a high-pass filter can use an inductor to block low frequencies while letting high frequencies pass — the specific combination and component values determine exactly where the filter's cutoff frequency sits.
The interaction between inductive and capacitive reactance also creates resonance, a special condition where the two reactances become equal in magnitude and effectively cancel each other's frequency-dependent effects, leaving only the circuit's resistance to limit current — this resonant frequency is the fundamental principle behind radio tuning circuits, which use an adjustable capacitor or inductor to shift the resonant frequency to match and select a desired radio station's broadcast frequency while rejecting others.
An inductor opposes changes in current, and at higher frequencies the current changes direction more rapidly, so the inductor generates a stronger opposing voltage — resulting in higher reactance.
Inductance (L, in henries) is a fixed physical property of the coil itself, while inductive reactance (XL, in ohms) depends on both the inductance and the frequency of the AC signal passing through it.
No — at DC (0 Hz), inductive reactance is zero, since there's no changing current to oppose. This calculator is intended for AC circuit analysis.