About the Capacitive Reactance Calculator
A capacitor blocks direct current but lets alternating current through more easily as the frequency rises. Its opposition to the alternating current is called capacitive reactance, XC, measured in ohms. This calculator takes the capacitance and the frequency and gives XC. If you add a voltage it also shows how much current would flow. Type the capacitance and the frequency, and optionally the voltage and the capacitive reactance appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Capacitive Reactance Calculator
- 1Enter the capacitance and the frequency, and optionally the voltage.
- 2Pick the units or options from the menus if the capacitive reactance tool offers them.
- 3Read the capacitive reactance in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the capacitive reactance
Capacitive reactance sets the cut-off of filters, the size of coupling capacitors in audio circuits and the amount of current that a capacitor dropper power supply can deliver. It also explains why a big capacitor across a power rail kills high-frequency noise.
Opposite to a coil, a capacitor's reactance falls as the frequency rises. In a perfect capacitor the current leads the voltage by 90 degrees, and no power is turned into heat, only stored and returned.
How the capacitive reactance is worked out
XC = 1 ÷ (2π × frequency × capacitance). At very low frequency XC is very large, and at very high frequency it is small. A 10 microfarad capacitor at 50 Hz has a reactance of 1 ÷ (2π × 50 × 0.00001) = 318.3 Ω. A 1 µF capacitor at 1 kHz has 159.2 Ω. With 230 V across the 10 µF capacitor at 50 Hz the current would be about 0.72 A.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Capacitance from pF to F
- Current at a given voltage
- Angular frequency shown
Mistakes to avoid with capacitive reactance
Make sure the capacitance is in the right unit; a value in nanofarads typed as microfarads makes the answer a thousand times too small. Real capacitors also have series resistance and inductance, so at very high frequency they stop behaving like ideal capacitors.
On phone and computer
On a phone, type into the boxes one after another and read the capacitive reactance underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the capacitive reactance move. The capacitive reactance calculator works the same on both. Compare it with Inductive Reactance Calculator, choose a part with Capacitor Calculator, find the charging time with RC Time Constant Calculator, and change the unit of the frequency with Frequency Converter.
Features
- Falls as frequency rises
- Check the unit
- Real parts have losses
- Clear messages when the capacitive reactance inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate capacitive reactance?
XC = 1 ÷ (2π × frequency × capacitance). At very low frequency XC is very large, and at very high frequency it is small. A 10 microfarad capacitor at 50 Hz has a reactance of 1 ÷ (2π × 50 × 0.00001) = 318.3 Ω. A 1 µF capacitor at 1 kHz has 159.2 Ω. With 230 V across the 10 µF capacitor at 50 Hz the current would be about 0.72 A.
What is the formula for capacitive reactance?
XC = 1 ÷ (2π × frequency × capacitance). At very low frequency XC is very large, and at very high frequency it is small. The capacitive reactance calculator applies it exactly and rounds only the displayed answer to six significant figures.
What happens at DC?
The frequency is 0, so XC is infinite: the capacitor passes no steady current.
Do reactances add?
Reactances of the same kind add in series. XL and XC cancel each other, since they act in opposite senses; that is how resonance arises.
What is the phase relation?
In an ideal capacitor, the current leads the voltage by 90 degrees.
Is this capacitive reactance calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.