Reactance Calculator

Reactance is the way inductors and capacitors oppose alternating current, and it is one of the foundational ideas in electronics and electrical engineering. Unlike a plain resistor, whose opposition is the same at any frequency, an inductor or capacitor pushes back by an amount that changes with frequency, and this calculator works out exactly how much. Enter the frequency along with an inductance and a capacitance, and it returns the inductive reactance XL and the capacitive reactance XC, both in ohms, updating as you type. The two behave in opposite ways, which is the heart of why they are so useful. Inductive reactance grows as frequency rises, because a faster-changing current meets more opposition from an inductor's magnetic field, so inductors tend to block high frequencies and pass low ones. Capacitive reactance does the reverse, falling as frequency rises, so capacitors pass high frequencies and block low ones, including direct current. That opposing behaviour is what makes filters, tuned circuits, crossovers, power supplies and timing circuits work, and being able to put real numbers on it is essential when you are designing or analysing a circuit. The calculator accepts inductance in millihenries and capacitance in microfarads, the units components are usually labelled in, and handles the conversions for you so you do not have to juggle powers of ten. Use it to find the reactance of a coil or capacitor at the mains frequency, to design a filter's corner frequency, to check an impedance, or simply to build intuition for how reactance and frequency relate. It is a dependable tool for engineers, technicians, hobbyists and students alike. The formulas and a worked example are below.

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