Inductive Reactance Calculator: X = 2 pi f L

The opposition of an inductor to alternating current.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Choose which quantity you want to find.

Enter the other values in the units shown.

The calculator gives the answer with the formula, the substituted numbers, and the answer in other units.

Formulas used

  • X_L = 2\pi fL
  • L = \frac{X_L}{2\pi f}

Worked example

With the default numbers in the calculator above:

  1. The formula, arranged to find the inductive reactance: inductive reactance = 2 pi x frequency x inductance
  2. Put the values in (every value in its SI unit): inductive reactance = 2 pi x 50 x 0.1
  3. The answer: inductive reactance: 31.4159 ohm
  4. The same answer in other units: 0.0314159 kohm

Change the numbers in the calculator to see the full working, every step, for your own case.

A second worked example

A different case, with these numbers: What do you want to find? Frequency; Inductive reactance (leave it as it is if this is what you are finding) 31.4159 ohm; Inductance (leave it as it is if this is what you are finding) 0.1 H.

  1. The formula, arranged to find the frequency: frequency = (inductive reactance) / (2 pi x inductance)
  2. Put the values in (every value in its SI unit): frequency = (31.4159) / (2 pi x 0.1)
  3. The answer: frequency: 50 Hz
  4. The same answer in other units: 0.05 kHz; 5.0e-5 MHz

Common questions

What is the formula for inductive reactance?

Two pi times the frequency times the inductance. A 0.1 H coil at 50 Hz has a reactance of 31.4 ohm.

Does the reactance rise or fall with frequency?

It rises. An inductor passes low frequencies and blocks high ones.

Is reactance the same as resistance?

No. Reactance stores and returns energy and does not use power, while resistance turns it to heat.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: Any electrical text (reactance).

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