Capacitive Reactance Calculator — Xc = 1/(2πfC)
Find the capacitive reactance of a capacitor in an AC circuit — enter frequency and capacitance to get Xc, plus current and reactive power when voltage is supplied.
Hz
µF
V
Xc = 1 ÷ (2π × f × C) — opposition to AC current by the capacitor
- 1
Capacitance in F
10 × 10⁻⁶ = 0.00001 - 2
2π × f × C
2π × 1,000 × 0.00001 = 0.062832 - 3
Reactance Xc = 1 ÷ (2π f C)
1 ÷ 0.062832 = 15.9155
How does this calculator work?
Capacitive reactance Xc = 1/(2πfC) ohms — a 10 µF capacitor at 1 kHz has Xc = 1/(2π × 1000 × 10⁻⁵) ≈ 15.9 Ω. Xc halves when frequency doubles. Current leads voltage by 90°. Enter frequency and capacitance to get Xc, plus current and reactive power for any AC voltage.
Formula
How this is calculated
In a direct-current (DC) circuit, a capacitor blocks current once fully charged. In an alternating-current (AC) circuit, the capacitor continuously charges and discharges with the oscillating voltage, allowing current to flow. The opposition to this AC current is called capacitive reactance, Xc = 1 / (2π × f × C), measured in ohms. Unlike resistance, reactance does not dissipate energy as heat — it stores and returns it every half cycle.
Capacitive reactance decreases with increasing frequency and increasing capacitance: at zero frequency (DC) reactance is infinite (open circuit); at very high frequency it approaches zero (short circuit). Doubling either f or C halves Xc. This frequency-dependence is exploited in filters — a capacitor passes high frequencies (low Xc) and blocks low ones (high Xc), forming the basis of high-pass filters.
In a purely capacitive circuit, current leads voltage by 90°: the current peaks one quarter-cycle before the voltage. This phase relationship is why reactive power Q = V²/Xc is measured in volt-amperes reactive (VAR) rather than watts — no average power is dissipated. The impedance of a real capacitor also includes a small equivalent series resistance (ESR), which is not modelled here; ESR is significant only near the self-resonant frequency of the component.
Frequently asked questions
A higher frequency means the voltage changes more rapidly, causing more charge to flow in and out of the capacitor every second — which is a larger current for the same voltage, i.e. lower opposition. Because Xc = 1/(2πfC), reactance is inversely proportional to frequency.
Resistance dissipates energy as heat and is independent of frequency. Reactance stores and returns energy (in an electric field for a capacitor, in a magnetic field for an inductor) and is strongly frequency-dependent. Both are measured in ohms, but only resistance causes real power loss.
Theoretically as frequency approaches infinity, Xc → 0 (a short circuit). Practically, every capacitor has a self-resonant frequency above which it behaves more like an inductor. For good bypass performance, choose a capacitor whose self-resonant frequency is above your highest signal frequency of interest.
TG we-Calculate Editorial Team. (2026). Capacitive Reactance Calculator — Xc = 1/(2πfC) [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/capacitive-reactance-calculator
TG we-Calculate Editorial Team. "Capacitive Reactance Calculator — Xc = 1/(2πfC)." TG we-Calculate. 2026. https://we-calculate.com/calculator/capacitive-reactance-calculator.
TG we-Calculate Editorial Team, "Capacitive Reactance Calculator — Xc = 1/(2πfC)," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/capacitive-reactance-calculator
@misc{wecalculate_capacitive_reactance_calculator, title = {Capacitive Reactance Calculator — Xc = 1/(2πfC)}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/capacitive-reactance-calculator}}, year = {2026}, note = {TG we-Calculate} }
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