Reactance Calculator
Inductive and capacitive reactance at any frequency, plus the frequency at which the two are equal and cancel.
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The formula
X_L = 2πfL X_C = 1 ÷ (2πfC)
Both are measured in ohms but neither dissipates power — reactance stores energy and gives it back. The two move in opposite directions with frequency, which is why every filter, tuned circuit and crossover in existence is built from the pair.
What to watch out for
Reactance is opposition measured in ohms, but it is not resistance:
- It dissipates nothing. A resistor turns electrical energy into heat. A reactance stores it in a field and returns it next half-cycle, which is why a purely reactive load draws current but consumes no power.
- It shifts the phase. Inductive reactance makes current lag voltage by 90°, capacitive makes it lead by 90°. That is why they subtract rather than add.
- It depends on frequency. At DC an inductor is a wire and a capacitor is an open circuit. At high frequency they swap roles.
Frequently Asked Questions
What is the formula for inductive reactance?
X_L = 2πfL. A 10 mH inductor at 1 kHz presents about 62.8 Ω. Reactance rises with frequency, so the same inductor at 10 kHz presents 628 Ω.
What is capacitive reactance?
X_C = 1 ÷ (2πfC). A 1 µF capacitor at 1 kHz presents about 159 Ω. It falls as frequency rises — the opposite of an inductor.
Why do the two reactances subtract?
Because they shift the current in opposite directions — an inductor makes it lag by 90°, a capacitor makes it lead by 90°, so they are 180° apart. When they are equal in magnitude they cancel completely, which is resonance.