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Application Mode

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Select a mode and enter your circuit parameters to calculate the required capacitor size.

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About

Undersized capacitors cause excessive ripple voltage in power supplies, leading to audible hum in audio circuits and logic errors in digital systems. Oversized capacitors increase inrush current, stress rectifier diodes, and waste board space. This calculator determines the minimum capacitance C for four common design scenarios: smoothing (filter) capacitors after rectification, decoupling capacitors for transient load demands, RC timing circuits, and energy storage applications. All results include automatic rounding to the nearest standard E-series value and a voltage derating recommendation at 50% to 80% of rated voltage per industry practice.

Formulas assume ideal capacitor behavior. Real-world performance degrades with ESR (equivalent series resistance), temperature drift, and aging. Electrolytic capacitors lose up to 20% capacitance over 10 years at rated temperature. Ceramic capacitors (Class II, X7R/X5R) exhibit DC bias derating - a 10µF rated part may deliver only 4µF at 80% of rated voltage. Always verify against the manufacturer datasheet.

Formulas

The calculator implements four distinct sizing equations depending on the selected application mode.

Smoothing (Full-Wave Rectifier):

C = I_load2 ⋅ f ⋅ V_ripple

Smoothing (Half-Wave Rectifier):

C = I_loadf ⋅ V_ripple

Decoupling Capacitor:

C = I_transient ⋅ ΔtΔV

RC Timing (Time Constant):

τ = R ⋅ C → C = τR

Energy Storage:

E = 12 ⋅ C ⋅ V² → C = 2 ⋅ EV²

Capacitive Reactance:

X_c = 12π ⋅ f ⋅ C

Where C = capacitance in F, I_load = DC load current in A, f = AC mains frequency in Hz, V_ripple = peak-to-peak ripple voltage in V, I_transient = transient current demand in A, Δt = transient duration in s, ΔV = maximum allowed voltage drop in V, τ = time constant in s, R = resistance in Ω, E = stored energy in J, X_c = capacitive reactance in Ω.

Reference Data

Capacitor Type	Capacitance Range	Voltage Range	Typical ESR	Temp. Range	Tolerance	Lifespan	Best Use
Aluminum Electrolytic	0.1µF - 1F	6.3 - 500V	0.01 - 5Ω	−40 to +105°C	±20%	2000 - 10000h	Power supply filtering
Ceramic (C0G/NP0)	0.5pF - 100nF	10 - 200V	< 0.01Ω	−55 to +125°C	±5%	> 50yr	Precision timing, RF
Ceramic (X7R)	100pF - 100µF	6.3 - 100V	0.005 - 0.05Ω	−55 to +125°C	±10%	> 50yr	Decoupling, bypass
Ceramic (Y5V)	10nF - 100µF	6.3 - 50V	0.01 - 0.1Ω	−30 to +85°C	+22/−82%	> 30yr	Non-critical bulk bypass
Film (Polyester/PET)	1nF - 10µF	50 - 1000V	0.005 - 0.1Ω	−55 to +125°C	±5%	> 100000h	Audio, AC coupling
Film (Polypropylene/PP)	100pF - 10µF	100 - 2000V	0.001 - 0.05Ω	−55 to +105°C	±1%	> 100000h	Snubber, resonant circuits
Tantalum	0.1µF - 1000µF	2.5 - 50V	0.05 - 3Ω	−55 to +125°C	±20%	> 20yr	Low-profile decoupling
Polymer (Solid Aluminum)	10µF - 560µF	2.5 - 25V	0.005 - 0.03Ω	−55 to +105°C	±20%	> 10000h	CPU/GPU VRM decoupling
Mica	1pF - 10nF	100 - 1000V	< 0.01Ω	−55 to +200°C	±1%	> 50yr	RF, high-frequency filters
Supercapacitor (EDLC)	0.1F - 3000F	2.5 - 5.5V	0.01 - 1Ω	−40 to +65°C	±20%	500000 cycles	Energy backup, pulse loads
Glass	0.5pF - 1000pF	100 - 500V	< 0.005Ω	−55 to +200°C	±1%	> 50yr	Military, aerospace
Vacuum	1pF - 5000pF	up to 60kV	< 0.001Ω	−55 to +85°C	±5%	> 30yr	RF transmitters, MRI

Frequently Asked Questions

Voltage derating extends capacitor lifespan and improves reliability. Operating an electrolytic capacitor at its full rated voltage accelerates dielectric oxide degradation. Industry practice recommends using no more than 50% to 80% of the rated voltage. For example, a 25V rated capacitor in a 12V circuit operates at 48% derating, which is ideal. NASA and military standards (MIL-STD-198) mandate 50% derating for mission-critical applications.

ESR (Equivalent Series Resistance) causes additional voltage drop under load: V_drop = I × ESR. A 1000μF electrolytic with 0.5Ω ESR carrying 2A ripple current loses an additional 1V. This means actual ripple is higher than the formula predicts. In practice, increase calculated capacitance by 20 - 50% to compensate, or select low-ESR polymer capacitors for demanding applications.

A full-wave rectifier charges the capacitor twice per AC cycle (at 2f), so the capacitor discharges for a shorter period between peaks. This halves the required capacitance compared to half-wave rectification for the same ripple voltage. A 50Hz mains supply produces 100Hz ripple with full-wave and 50Hz ripple with half-wave rectification.

Class II ceramics (X7R, X5R, Y5V) lose capacitance as applied DC voltage increases. A 10μF X7R capacitor rated at 25V may provide only 4 - 6μF at 20V DC bias. This is not captured by the formula. Always consult manufacturer DC bias curves. Class I ceramics (C0G/NP0) are immune to this effect but are limited to small capacitance values.

The calculator rounds to E12 series values by default (1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2). E12 corresponds to ±10% tolerance parts, which covers the majority of electrolytic and ceramic capacitors. The rounding always selects the next value upward to ensure the minimum required capacitance is met.

Capacitors in parallel add directly: C_total = C₁ + C₂ + ... + C_n. This is a standard practice to hit exact values or to reduce effective ESR (ESR halves when paralleling two identical capacitors). The calculator provides the total required value. You can split it across multiple parallel parts if a single component is unavailable or too large.