Capacitive reactance calculator

Type f [Hz] and C [F]. The calculator computes Xc = 1/(2πfC): 50 Hz and 10 µF (1e-5 F) is about 318 Ω, and 60 Hz at the same C is about 265 Ω. Zero farads does not divide.

Coil reactance: XL = 2πfL. Resonance: f = 1/(2π√LC).

Inputs

Result

Frequency f (Hz) and Capacitance C (F). The result shows up here.

How it works

Xc = 1/(2πfC) f ↑ ⇒ Xc ↓ C
Capacitor reactance falls with frequency: Xc = 1/(2πfC).

Capacitive reactance is Xc = 1 / (2π f C). At 50 Hz and 1e-5 F (10 µF) you get about 318 Ω. At 60 Hz and the same C about 265 Ω. At 50 Hz and 1e-4 F about 31.8 Ω. Higher f, smaller Xc. At 1000 Hz and 1e-6 F about 159 Ω. At 50 Hz and 4.7e-4 F about 6.8 Ω.

The form has two fields: f in hertz and C in farads. Type 10 µF as 1e-5, not as 10. The result is in ohms. A comma, a period, and 1e-5 are the same C. 0.00001 also parses; 1e-5 is easier.

f and C must be positive. Zero does not divide. Both fields need a number before 318 Ω can appear. Reactance XL at one f and one L. Xc enters |Z| in AC; it does not replace R on the Ohm page.

XL = 2πfL is on the neighbouring page and rises with f. Here Xc falls with f. C = Q/U is capacitance in farads, not reactance. Resonance when Xc = XL is on f = 1/(2π√(LC)).

At 1000 Hz and 1e-5 F you get about 15.9 Ω. This calculator does not build a network. It takes one f and one C.

Type 50 and 1e-5, click Calculate, and match about 318 Ω. Then jump to 60 Hz at the same C and see 265 Ω. The header symbol does not charge the plates.

How to use

  1. In the first field enter f in hertz, for example 50. US mains is 60.
  2. In the second field enter C in farads, for example 1e-5. 10 µF is 1e-5, not 10.
  3. Click Calculate. The calculator computes 1/(2πfC). 50 Hz and 1e-5 F give about 318 Ω.
  4. f and C must be positive. Zero does not divide. Both fields need a number.
  5. For XL, open inductive reactance. Resonance when Xc = XL is on f = 1/(2π√(LC)).

Formula

XC = 1 / (2πfC)

f > 0, C > 0. Unit of Xc: ohm (Ω).

Xc, f, and C for AC capacitance

Xc falls with f: Xc = 1/(2πfC). 50 Hz and 1e-5 F (10 µF) is about 318 Ω. 60 Hz and the same C is about 265 Ω.

Xc
Capacitive reactance [Ω]. 1 / (2π × 50 × 1e-5) ≈ 318 Ω. It shrinks as f grows.
f
Frequency [Hz]. 50 or 60. Zero does not divide.
C
Capacitance [F]. 10 µF is 1e-5, not 10. C must be positive.
π
The constant in 2πfC in the denominator. Not the XL = 2πfL card.

Real-life examples

Example 1

f = 50 Hz, C = 1e-5 F -> Xc ≈ 318 Ω.

Example 2

f = 60 Hz, C = 1e-5 F -> Xc ≈ 265 Ω.

Example 3

f = 50 Hz, C = 1e-4 F -> Xc ≈ 31.8 Ω.

Example 4

f = 1000 Hz, C = 1e-6 F -> Xc ≈ 159 Ω.

Example 5

f = 1000 Hz, C = 1e-5 F -> Xc ≈ 15.9 Ω.

Example 6

f = 1e6 Hz, C = 1e-9 F -> Xc ≈ 159 Ω.

Example 7

f = 50 Hz, C = 4.7e-4 F -> Xc ≈ 6.8 Ω.

Example 8

f = 20 Hz, C = 1e-4 F -> Xc ≈ 79.6 Ω.

Ways to use this calculator

  • You compute about 318 Ω from 50 Hz and 1e-5 F.
  • You keep C and jump to 60 Hz: about 265 Ω.

Related calculators

Capacitance C = Q/U
The capacitance that goes into capacitive reactance.
Resonance frequency
LC resonance, the frequency where Xc equals XL.
Inductive reactance calculator XL = 2πfL
Coil reactance grows with frequency and inductance.
Faraday induction
Induced EMF from how fast the magnetic flux is changing.
Transformer calculator U2 = U1·(n2/n1)
Secondary voltage of an ideal transformer
Transformer secondary turns n2 = n1·(U2/U1)
Secondary turns from the two voltages and n1.

All physics calculators

Frequently asked questions

How much Xc at 50 Hz and 1e-5 F?

Reactance is about 318 Ω. You compute 1 / (2π × 50 × 1e-5). 50 Hz mains, a 10 µF capacitor.

Which units do I type?

Frequency f [Hz], capacitance C [F]. Result Xc [Ω]. Type 10 µF as 1e-5, not as 10.

What if C = 0?

The calculator refuses zero farads. Xc = 1/(2πfC) at zero C does not exist.

How is Xc different from XL?

Xc falls as f rises. XL = 2πfL grows with f. Another card and another formula, even though both give ohms.

How is this different from C = Q/U?

Here reactance in an AC circuit. There capacitance from charge and voltage, with no frequency.

How much at 1000 Hz and 1e-6 F?

You get about 159 Ω. At 1000 Hz and 1e-5 F it is about 15.9 Ω: ten times C, one tenth the Xc.

Does a comma in 0.00001 work?

Yes. 0.00001, 0,00001 and 1e-5 are the same C [F]. 1e-5 is easier.

When is Xc = XL?

At LC resonance. f = 1/(2π√(LC)) lives on the resonance page. Here you only compute Xc, with no L.

How much at 50 Hz and 4.7e-4 F?

Reactance is about 6.8 Ω. A large capacitor on mains, a small Xc.

Is this Ohm resistance R?

No. Xc is reactance, ohms without Joule heat. R = U/I on DC is another calculator.

Knowledge sources

The formula is the school one. Units follow SI; NIST SP 330 and BIPM define the measures, not your result.

Page updated in 2026.