Capacitive Reactance Calculator (Xc)
Choose what to solve for, then enter the other two values with their units. The calculator uses Xc = 1 / (2π f C) and shows the answer in a convenient unit.
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Formula
Xc = 1 / (2 × π × f × C)
Rearranged: f = 1 / (2 × π × Xc × C) and C = 1 / (2 × π × f × Xc). Use f in hertz, C in farads and Xc in ohms; the calculator converts your units first. Only the two inputs needed for the chosen mode are used.
Worked example
A 1 µF capacitor at 1 kHz:
Xc = 1 / (2π × 1000 × 0.000001) = 1 / 0.0062832 = 159.15 Ω
Other checks: 100 nF at 50 Hz gives 31.83 kΩ. To get 100 Ω at 1 kHz you need 1.5915 µF.
Frequently asked questions
What is the capacitive reactance formula?
Xc = 1 / (2π × f × C), with f in hertz and C in farads, gives Xc in ohms. For 1 µF at 1 kHz: 1 / (2π × 1000 × 0.000001) = 159.15 Ω.
Why does reactance fall as frequency rises?
A faster alternating signal moves charge on and off the plates more often, so more current flows for the same voltage. The same 1 µF is 159.15 Ω at 1 kHz but only 15.9 Ω at 10 kHz. At DC (0 Hz) the reactance is infinite.
How do I find the capacitor for a given reactance?
Choose Capacitance C as the unknown. To get 100 Ω at 1 kHz you need C = 1 / (2π × 1000 × 100) = 1.5915 µF.
Is reactance the same as resistance?
Both are measured in ohms, but reactance stores and returns energy instead of turning it into heat, and the current leads the voltage by 90 degrees. Combined with resistance it forms the impedance, Z = √(R² + X²).
Can I use this for safety or final design sign-off?
No. This calculator is for learning and design checks, not safety certification. Real capacitors have tolerance, ESR and parasitic inductance that change their behaviour, especially at high frequency.