Calculator
Example Data Table
| Frequency | Reactance | Calculated Capacitance | Common Use |
|---|---|---|---|
| 50 Hz | 3183.10 Ω | 1 µF | Low frequency filter check |
| 60 Hz | 26525.82 Ω | 0.1 µF | Line frequency estimate |
| 1 kHz | 1591.55 Ω | 0.1 µF | Audio circuit sizing |
| 100 kHz | 15.92 Ω | 0.1 µF | Switching circuit check |
Formula Used
Capacitive reactance is calculated with this formula:
Xc = 1 / (2πfC)
When reactance and frequency are known, rearrange it:
C = 1 / (2πfXc)
Where C is capacitance in farads, f is frequency in hertz, and Xc is capacitive reactance in ohms.
Tolerance range: Cmin = C × (1 - tolerance / 100) and Cmax = C × (1 + tolerance / 100).
Stored energy: E = 0.5 × C × V². Stored charge: Q = C × V.
Optional RC values use τ = R × C and fc = 1 / (2πRC).
How to Use This Calculator
- Enter the target capacitive reactance.
- Select the matching reactance unit.
- Enter the circuit frequency.
- Choose the answer unit you prefer.
- Add tolerance, voltage, and resistance if needed.
- Press Calculate to view results above the form.
- Use CSV or PDF buttons to export the same calculation.
Capacitance From Reactance Guide
Why Capacitance From Reactance Matters
Capacitive reactance shows how strongly a capacitor opposes alternating current. The opposition changes with frequency. A higher frequency needs less capacitance for the same reactance. A lower frequency needs more capacitance. This calculator turns that relationship into a fast design check.
Electrical Uses
Designers use this value in filters, timing networks, coupling stages, audio crossovers, power factor studies, and RF matching work. The result helps compare a target reactance with real capacitor values. It also helps avoid trial and error during early circuit planning. You can test different frequency units, reactance units, tolerance bands, and output units.
Better Component Choice
A calculated value is only the starting point. Real capacitors have tolerance, voltage limits, leakage, equivalent series resistance, and temperature drift. The tool adds tolerance bounds and optional energy details. These extra values help show whether a part has enough margin. They also show how much stored charge may exist at a selected voltage.
Practical Accuracy
The formula assumes an ideal capacitor and a sinusoidal signal. It does not include parasitic inductance or dielectric losses. At high frequency, those effects can become important. At low frequency, leakage and tolerance may dominate. Use the calculator for first sizing, then verify with datasheets and measurements. This is especially important in power electronics and RF circuits.
Reading the Result
The main answer is capacitance. The calculator also displays farads, millifarads, microfarads, nanofarads, and picofarads. This makes it easy to move between engineering notation and catalog values. When a voltage is entered, energy and charge are shown. When a resistor is entered, the RC time constant and cutoff frequency are estimated.
Good Workflow
Start with the required capacitive reactance. Enter the working frequency. Select units carefully. Add tolerance and voltage data when known. Press calculate. Review the recommended equivalent values for equal parallel or series capacitors. Export the result when you need records for reports, worksheets, or design notes. This simple process keeps calculations repeatable, clear, and easier to audit.
Safety Notes
Always choose a capacitor type suited to the circuit. Check ripple current, polarity, temperature rating, and safety approvals. For mains work, use approved X or Y safety capacitors only. When uncertain, ask a qualified electrical professional first.
FAQs
What is capacitive reactance?
Capacitive reactance is the opposition a capacitor gives to alternating current. It depends on frequency and capacitance. Higher frequency or higher capacitance lowers the reactance.
Which formula does this calculator use?
It uses C = 1 / (2πfXc). Frequency must be in hertz. Reactance must be in ohms. The answer is first found in farads.
Can I use kilohms or megohms?
Yes. Select the matching unit beside the reactance field. The script converts the value to ohms before applying the formula.
Why does capacitance decrease at higher frequency?
For the same reactance target, frequency and capacitance have an inverse relationship. When frequency rises, less capacitance is needed to create that reactance.
Does this include capacitor ESR?
No. The main formula assumes an ideal capacitor. Real capacitors include ESR, leakage, tolerance, and self resonance. Check datasheets for final selection.
What does the tolerance range mean?
The range shows possible capacitance values caused by component tolerance. A 10 percent capacitor may measure above or below the calculated nominal value.
Why enter voltage?
Voltage lets the calculator estimate stored charge, stored energy, and a suggested voltage rating using the derating factor. It does not replace safety review.
Can I export the calculation?
Yes. Use the CSV button for spreadsheet records. Use the PDF button for a simple printable report with inputs, formulas, and calculated results.