Capacitor Calculator — Charge, Energy & Reactance
Enter a capacitance value, the voltage across the capacitor and the signal frequency to get stored charge (Q = C × V), stored energy (E = ½ × C × V²), and capacitive reactance (Xc = 1 / (2π f C)).
Unit
V
Hz
Q = C × V
- 1
Capacitance in farads (uF × factor)
100 × 1e-6 = 0.0001 - 2
Stored charge Q = C × V
0.0001 × 12 = 0.001200
How does this calculator work?
A capacitor with capacitance C holds charge Q = C × V and energy E = ½ × C × V². In an AC circuit it shows reactance Xc = 1/(2πfC) ohms — lower at higher frequencies. Enter C (in any unit), voltage V and frequency f to see all three quantities instantly.
Formula
How this is calculated
A capacitor stores electric charge on two conductive plates separated by an insulating dielectric. When a voltage V is applied, the plates accumulate charge Q = C × V coulombs, where C is the capacitance in farads (F). Because charge builds up as voltage rises linearly from zero, the energy stored in the resulting electric field is E = ½ × C × V² joules — half of what simple multiplication would suggest, because the average voltage during charging is V/2.
In an AC circuit, a capacitor does not simply block current the way an open circuit does — it passes AC while opposing it with a frequency-dependent impedance called capacitive reactance, Xc = 1 / (2π f C), measured in ohms. At higher frequencies the capacitor offers less opposition, and at lower frequencies it offers more. At DC (f = 0) reactance is infinite and no current flows in steady state.
Select the unit that matches your component's label (µF, nF, pF are most common for discrete components; F or mF for supercapacitors). All results assume a linear, lossless capacitor with constant capacitance independent of voltage and temperature. Real capacitors have tolerances, leakage currents, and equivalent series resistance (ESR) that this calculator does not model.
Frequently asked questions
Ceramic capacitors are usually rated in nanofarads (nF) or picofarads (pF); electrolytic capacitors are usually in microfarads (µF). Select the matching unit so no manual conversion is needed.
Reactance Xc = 1/(2πfC) is inversely proportional to frequency. At higher frequencies the capacitor charges and discharges more rapidly, allowing more current through for the same voltage — so it appears as a lower impedance.
Yes for charge and energy — just enter the DC voltage. The reactance field requires a non-zero frequency; at DC a capacitor blocks steady-state current entirely (Xc → ∞ as f → 0), so the reactance result is only meaningful for AC signals.
TG we-Calculate Editorial Team. (2026). Capacitor Calculator — Charge, Energy & Reactance [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/capacitor-calculator
TG we-Calculate Editorial Team. "Capacitor Calculator — Charge, Energy & Reactance." TG we-Calculate. 2026. https://we-calculate.com/calculator/capacitor-calculator.
TG we-Calculate Editorial Team, "Capacitor Calculator — Charge, Energy & Reactance," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/capacitor-calculator
@misc{wecalculate_capacitor_calculator, title = {Capacitor Calculator — Charge, Energy & Reactance}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/capacitor-calculator}}, year = {2026}, note = {TG we-Calculate} }
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