Case 1
- Frequency
- 50Hz
- Capacitance
- 0.0001F
31.830989Ω
Open with these valuesCapacitive Reactance Calculator
318.309886Ω
Result: 318.309886 ΩA capacitor opposes alternating current less and less as the frequency rises: 10 µF is 265 Ω at 60 Hz but only 0.27 Ω at 60 kHz. Only the product of frequency and capacitance matters, so 1 µF at 1 kHz and 100 nF at 10 kHz give the same 159 Ω.
Worked examples
Case 2
- Frequency
- 60Hz
- Capacitance
- 0.00001F
265.258238Ω
Open with these valuesCase 3
- Frequency
- 1000Hz
- Capacitance
- 0.000001F
159.154943Ω
Open with these valuesHow it's calculated
Xc = 1 ÷ (2 × π × f × C)
- StepEnter the frequency of the signal in hertz.
- StepEnter the capacitance in farads — 10 µF is 0.00001.
- ResultRead the reactance in ohms; it falls as either input rises.
What this number means
The reactance falls as the frequency rises
The plates have less time to charge before the voltage reverses, so more current flows for the same voltage. 10 µF is 265 Ω at 60 Hz and only 0.27 Ω at 60 kHz; at direct current the reactance is infinite and the capacitor blocks entirely.
Ohms here are not a resistance
A capacitor turns no energy into heat — it stores charge and gives it back each half cycle. Its current leads the voltage by a quarter cycle, so resistance and reactance combine as Z = √(R² + Xc²) rather than by addition.
Only the product f × C appears in the formula
Ten times the frequency against a tenth of the capacitance leaves the reactance unchanged. That is why 1 µF at 1 kHz and 100 nF at 10 kHz both come out at 159.154943 Ω.
Commonly misread
Xc is 100 Ω and R is 100 Ω, so the circuit shows 200 Ω.
Reactance and resistance are a quarter cycle apart, so they add as Z = √(R² + Xc²). That is about 141 Ω, not 200 Ω.
My capacitor is 10 µF, so I enter 10.
The field takes farads: 10 µF is 0.00001. Entering 10 at 60 Hz returns 0.000265 Ω instead of 265 Ω.
At direct current the reactance drops to zero.
It goes the other way: at direct current the reactance is infinite and the capacitor blocks entirely.
Reference table
| Frequency, capacitance | What that is | Reactance |
|---|---|---|
| 50, 0.0001 | 100 µF on 50 Hz mains | 31.830989 |
| 60, 0.000047 | 47 µF motor-run capacitor | 56.437923 |
| 1000, 0.000001 | 1 µF at 1 kHz | 159.154943 |
| 10000, 0.0000001 | 100 nF at 10 kHz | 159.154943 |
| 60, 0.00001 | 10 µF on 60 Hz mains | 265.258238 |
Questions
What is capacitive reactance?
The opposition a capacitor offers to alternating current, measured in ohms. Unlike a resistor it turns no energy into heat — it stores charge and gives it back each half cycle.
Why does it fall as the frequency rises?
The plates have less time to charge before the voltage reverses, so more current flows for the same voltage. At direct current the reactance is infinite and the capacitor blocks entirely.
Can I add it to a resistance in the same circuit?
Not directly. The capacitor's current leads the voltage by a quarter cycle, so resistance and reactance combine as Z = √(R² + Xc²), not by simple addition.
Why do 1 µF at 1 kHz and 100 nF at 10 kHz agree?
Because only the product f × C appears in the formula. Ten times the frequency against a tenth of the capacitance leaves that product, and therefore the reactance, unchanged.
Sources and last check
Information, not professional advice.