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Capacitive Reactance Calculator

Find the magnitude of an ideal capacitor’s opposition to sinusoidal alternating current. Enter the AC frequency in hertz and capacitance in microfarads. This magnitude decreases as either frequency or capacitance increases. It is a reactance magnitude, not a resistance that necessarily turns electrical energy into heat. Use it within a complete AC circuit model that also includes resistance and any inductance.

Enter every field, including explicit zeros when permitted. Decimal and scientific notation are accepted; commas, fractions and blanks are rejected. Each input must be finite and no larger than 1 billion in absolute value. Observe the units and positive-value requirements below.

Capacitive reactance magnitude (Ω)31.83098862

How to use this calculator

  1. Match your inputs to the stated circuit model and field labels.
  2. Convert your quantities to the units printed next to each field.
  3. Select Calculate, or press Enter, and read the labeled results.

Formula and method

XC = 1/(2πfC), with C in farads.

The calculation runs in your browser. After changing an input, select Calculate again. Invalid inputs or undefined mathematical conditions hide the previous result so it cannot be mistaken for an answer to the new values.

Worked example

At 50 Hz with 100 µF = 0.0001 F, XC = 1/(2π×50×0.0001) = 100/π ≈ 31.83098862 Ω.

Limitations and safety

Ideal-component calculation only. Component tolerance, heating, parasitic effects and frequency limits are not modeled. This output does not establish component ratings, wiring compliance or a safe circuit design. Have consequential designs checked by a qualified professional; do not use this tool as instructions for working on energized equipment. DC, zero capacitance and capacitor self-resonance are outside this finite positive-frequency model.

The fields accept signed numerical input, but positive-only component values and nonnegative time or frequency requirements are enforced by the calculation. Read each error message before changing a value. Results use floating-point arithmetic and are shown to approximately 10 significant digits; component tolerances generally do not justify using all those digits in a physical design.

Frequently asked questions

What happens at DC?

In the ideal steady-state limit, capacitive reactance tends to infinity as frequency tends to zero. This tool requires a positive frequency.

Why are my units important?

The calculator uses exactly the units printed in the input labels. For example, a micro-unit is one millionth of a base unit, and a milli-unit is one thousandth. Entering a base-unit value into a prefixed-unit field changes the meaning of the input.

Does the answer establish a safe component rating?

No. The formula evaluates an ideal model. Ratings, tolerances, transients, installation requirements and environmental limits need a separate design assessment.

Review notes and reference

Reviewed October 3, 2026. The default worked example and an additional boundary or scaling check were tested against expected values. Validation checks included blanks, nonnumeric text and inputs outside the supported range. OpenStax University Physics formula reference provides the circuit theory behind this model. The text and worked example on this page are original.

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