Capacitor Size Calculator — Find Required Capacitance
Solve for the capacitance C you need — given stored energy, stored charge, a maximum ripple voltage for a power supply filter, or a desired reactance at a specific frequency.
What are you solving for?
J
V
In farads: 0.000013888889 F
- 1
Square the voltage
12² = 144 - 2
Required capacitance (µF)
2 × 0.001 ÷ 144 × 10⁶ = 13.8889C = 2E ÷ V², converted to µF
How does this calculator work?
Choose the right formula for your need: C = 2E/V² (energy storage), C = Q/V (charge), C = I/(f × ΔV) (ripple filter), or C = 1/(2πfXc) (target reactance). Enter your knowns and the calculator gives the required capacitance in µF, nF and pF. Always round up to the next standard component value and derate for voltage.
Formula
How this is calculated
The required capacitance depends on which electrical quantity you're designing for. For energy storage (e.g. a camera flash or hold-up circuit), rearrange E = ½CV² to get C = 2E / V². For a charge requirement Q at a known voltage, use C = Q / V. For a power-supply smoothing capacitor, the approximate ripple formula C = I / (f × ΔV) gives the capacitance needed to keep the output ripple below ΔV for a load current I at ripple frequency f (use 100 Hz for full-wave rectification of a 50 Hz mains, or 120 Hz for 60 Hz mains). For a filter or coupling capacitor with a specific impedance target, invert the reactance formula to get C = 1 / (2π f Xc).
All four formulas rearrange the standard capacitor relationships and assume ideal, linear components. Real capacitors carry a voltage-dependent capacitance (especially ceramics — up to 80% derating at rated voltage), tolerance (typically ±5–20%), and temperature coefficients. Always select a capacitor rated for at least 1.5× the maximum voltage in the circuit and consider the next standard value above the calculated minimum (E6, E12 or E24 series values are most common).
Ripple sizing applies to the DC output smoothing capacitor in a simple rectifier circuit. It uses the linear-discharge approximation, which is accurate enough for small ripple fractions but becomes less precise when ripple is a large fraction of the supply voltage.
Frequently asked questions
In a full-wave rectifier the ripple frequency is twice the mains frequency: 100 Hz for 50 Hz mains (Europe) or 120 Hz for 60 Hz mains (Americas). Half-wave rectifiers use the mains frequency directly (50 or 60 Hz), requiring a larger capacitor for the same ripple.
No — capacitors are sold in standard E6, E12 or E24 values. Round up to the next standard value above your calculated minimum. For critical circuits, also account for tolerance: a 100 µF capacitor rated ±20% could measure as low as 80 µF, so you may need a larger nominal value.
Reactance Xc = 1/(2πfC) is the AC impedance of the capacitor at frequency f. A high reactance means the capacitor passes little AC current at that frequency (useful for bypassing high frequencies, blocking DC-bias, etc.). Use the reactance mode when you have a filter or coupling requirement specified as an impedance.
TG we-Calculate Editorial Team. (2026). Capacitor Size Calculator — Find Required Capacitance [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/capacitor-size-calculator
TG we-Calculate Editorial Team. "Capacitor Size Calculator — Find Required Capacitance." TG we-Calculate. 2026. https://we-calculate.com/calculator/capacitor-size-calculator.
TG we-Calculate Editorial Team, "Capacitor Size Calculator — Find Required Capacitance," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/capacitor-size-calculator
@misc{wecalculate_capacitor_size_calculator, title = {Capacitor Size Calculator — Find Required Capacitance}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/capacitor-size-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?