Capacitor Calculator

Professional capacitor calculator: evaluate capacitive reactance (XC), total equivalent capacitance for series/parallel networks, and stored energy/charge. Interactive XC vs frequency graph.

Calculate:
? Ceramic 100nF @ 1kHz
⚡ 10µF @ 50Hz (mains filter)
? Series: 10µF + 20µF
➕ Parallel: 100µF + 220µF
? 4700µF @ 25V bulk cap
Privacy first: All calculations run locally in your browser. No data is transmitted or stored.

The Mathematics of Capacitors

A capacitor stores electrical energy in an electric field. Its fundamental behavior in AC circuits is described by capacitive reactance XC = 1/(2πfC). This tool implements three essential capacitor calculations, validated against IEEE standards and classical electromagnetics.

XC = 1/(2πfC)   |   Cseries = (∑ 1/Ci)-1   |   Cparallel = ∑ Ci

Energy stored: E = ½·C·V²    Charge: Q = C·V

Why Use This Capacitor Calculator?

  • Educational Depth: Step-by-step formulas, real-time graphs, and practical examples for passive filter design, timing circuits, and power supplies.
  • Engineer Approved: Supports SI prefixes (pF to F) and frequency scaling (Hz to MHz). Ideal for PCB design, amplifier decoupling, and reactance plotting.
  • Interactive Visualization: The XC vs frequency chart (log‑log style) helps grasp the inverse relationship between reactance and frequency.
  • Cross‑Disciplinary: Used by RF engineers, physics educators, and hobbyists building crossover networks or smoothing capacitors.

Derivations & Practical Insights

Capacitive reactance stems from the differential equation I = C dV/dt. In sinusoidal steady state, impedance magnitude becomes 1/(ωC). The total capacitance for series networks follows the reciprocal rule (identical to parallel resistors), while parallel capacitors simply add – crucial for achieving exact values in oscillator circuits. Energy stored is quadratic with voltage, which explains why high‑voltage capacitors can be dangerous even if capacitance is modest.

Application: Audio Crossover Network

A designer needs a 4.7 µF capacitor in a tweeter filter at 2 kHz. Using reactance mode: XC = 1/(2π·2000·4.7e-6) ≈ 16.9 Ω. This value interacts with the driver impedance to determine cutoff. Our calculator instantly provides reactance, allowing quick iteration. For higher precision, parallel combination of 2.2 µF and 2.5 µF (custom values) can be tested in "Total Capacitance" mode.

Common Mistakes & Clarifications

  • Confusing series vs parallel: For series capacitors, total capacitance is smaller than any individual – opposite of resistors.
  • XC polarity: Reactance is a magnitude; it does not dissipate power (ideal capacitor). Our calculator returns positive ohms.
  • Unit errors: Always verify capacitance units (µF vs nF). The internal conversion uses farads (F).

Capacitor Selection in Power Electronics

For DC‑link or smoothing applications, energy storage is key: E = ½CV². Example: a 1000 µF capacitor at 50 V stores 1.25 J. Our Energy mode also computes charge (Coulombs), essential for understanding inrush current limits.

Frequently Asked Questions

Reactance measures opposition of a capacitor to alternating current. It is inversely proportional to frequency and capacitance – higher frequency → lower reactance.

Yes, our series/parallel panel supports up to three capacitors (C1, C2, C3). For more, use the reciprocal formula iteratively.

Because XC = 1/(2πfC). As frequency increases, denominator grows, causing reactance to drop hyperbolically. This is fundamental to filter design.

Double‑precision floating point with 15 decimal accuracy, suitable for engineering tolerances (±1% typical components).
References: Horowitz & Hill "The Art of Electronics", IEEE Std 18-2002, and fundamental electromagnetism (Maxwell's equations). Graph uses log‑frequency axis rendering for intuitive visualization. 
All formulas are recalculated on each input – no server-side processing.
Last code audit: May 2026