Resistors oppose current plainly, but inductors and capacitors oppose it with a twist — their opposition, called reactance, depends on frequency. An inductor's reactance grows with frequency: X_L = 2πfL, so a coil barely notices 60 Hz house current but walls off radio frequencies. A capacitor does the opposite: X_C = 1 ÷ (2πfC), blocking DC entirely (zero frequency means infinite reactance) while waving high frequencies through. Together with resistance, reactance forms impedance — the full AC opposition.

Crossover networks in speakers split bass to the woofer and treble to the tweeter using exactly this frequency dependence, and radio tuners select stations by resonating an inductor-capacitor pair where the two reactances cancel. At resonance, X_L equals X_C and the circuit's opposition collapses to pure resistance. This calculator evaluates either formula's multiplication: for inductive reactance, type 2πf — at 60 Hz, 2 × π × 60 ≈ 376.99 — in the Variable A box and the inductance L in henries in the Variable B box. A 0.1 H coil gives 376.99 × 0.1 ≈ 37.7 ohms. For capacitive reactance, type 1 ÷ (2πfC)'s factors instead: enter 1 ÷ C in A and 1 ÷ (2πf) in B.

With the pre-filled defaults — Variable A 10, Variable B 5 — the Reactance Calculator returns Result 50.0000. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.