Capacitors are everywhere in electronics — power supplies, filters, timing circuits, energy storage. Our capacitance calculator handles the five most common capacitor calculations in one tool: parallel-plate capacitance from physical dimensions, series capacitor combinations (1/C = Σ1/Cᵢ), parallel combinations (C = ΣCᵢ), RC time constants (τ = R × C), and stored energy (E = ½CV²). Each mode uses the appropriate physics and reports results in all four common capacitance units (F, µF, nF, pF) so you can match whatever notation your circuit diagram or datasheet uses.
Choose parallel plate, series, parallel, RC time, or energy.
Each mode uses different inputs — fill the ones for your selected mode.
See capacitance in F, µF, nF, pF plus mode-specific outputs.
A parallel-plate capacitor's capacitance is proportional to plate area and dielectric constant, inversely proportional to plate separation. Capacitors in series combine like resistors in parallel (the total is less than the smallest); capacitors in parallel combine additively. The RC time constant tells you how fast a capacitor charges or discharges through a resistor — voltage reaches 63% in 1τ and 99% in 5τ. Stored energy scales with the square of voltage.
C = ε₀εᵣA/d • Series: 1/C = Σ1/Cᵢ • Parallel: C = ΣCᵢ • τ = RC • E = ½CV²
Series capacitors: total capacitance is always LESS than the smallest individual capacitor
Parallel capacitors: total capacitance is the SUM of all individual capacitors
RC time constant τ = R × C — voltage reaches 63% of final in 1τ, 99% in 5τ
Stored energy E = ½CV² scales with voltage² — doubling V quadruples energy
Common dielectric constants: vacuum 1, air 1.0006, glass ~5, water 80, ceramic 10-3000
Capacitors in series increase voltage rating; in parallel they increase capacitance
Electrolytic capacitors are polarized — connect them backwards and they fail catastrophically
Capacitors are among the most widely used passive components in electronics, appearing in everything from smartphone power supplies to industrial motor drives. A single circuit board may contain hundreds of capacitors performing filtering, energy storage, timing, coupling, and decoupling functions. Calculating capacitance correctly is essential for circuit performance — an undersized filter capacitor causes excessive ripple, while an oversized one wastes board space and budget. The parallel-plate capacitance formula C = epsilon-zero times epsilon-r times A divided by d governs basic capacitor physics, but real-world design also requires computing series and parallel combinations, RC time constants for timing circuits, and stored energy for power supply hold-up calculations. Common capacitance values span twelve orders of magnitude, from single-digit picofarads in RF circuits to thousands of microfarads in audio amplifiers. This capacitance calculator handles all five core calculations — parallel-plate sizing, series combinations, parallel combinations, RC time constants, and energy storage — and reports results in farads, microfarads, nanofarads, and picofarads simultaneously.
Capacitors store electrical energy in an electric field between two conductors. They're used everywhere:
Understanding capacitance lets you size capacitors correctly for any of these applications without trial and error.
One thing that trips up new electronics engineers: capacitors combine the OPPOSITE way from resistors.
Resistors in series add; capacitors in series combine like resistors in parallel (smaller). Resistors in parallel combine like 1/(1/R₁+1/R₂); capacitors in parallel just add.
If you ever forget, remember that series capacitors are 'pulled apart' by the geometry, reducing effective capacitance, while parallel capacitors stack effective area, increasing it.
Parallel-plate capacitance is calculated with C = ε₀ × εᵣ × A / d, where:
NIST fixes ε₀ at 8.8541878188×10⁻¹² F/m. For a 0.01 m² plate area, a 0.001 m gap, and vacuum (εᵣ = 1), C = 8.854×10⁻¹² × 1 × 0.01 / 0.001 = 8.854×10⁻¹¹ F, or 88.5 pF.
Capacitance rises with larger plate area and higher dielectric constant, and falls as the plates move apart, as HyperPhysics (Georgia State University) explains.
The SI unit of capacitance is the farad (F), defined by BIPM as one coulomb of stored charge per volt of potential difference (1 F = 1 C/V).
The farad is enormous for everyday electronics, so most real capacitors are rated in:
Per the SI Brochure, the farad is a coherent derived unit expressible as s⁴·A²·kg⁻¹·m⁻². This calculator reports every result in F, µF, nF, and pF at once so you can match whatever notation a datasheet or schematic uses.
For capacitors in series, the reciprocals add: 1/C_total = 1/C₁ + 1/C₂ + 1/C₃, so the total is always less than the smallest member. Two equal capacitors of 2 µF in series give 1 µF.
For capacitors in parallel, the values add directly: C_total = C₁ + C₂ + C₃, so 1 µF plus 2 µF equals 3 µF.
As HyperPhysics notes, this is exactly the reverse of resistor combination rules. Series connection reduces capacitance but increases the effective voltage rating; parallel connection increases capacitance while keeping the voltage rating of the weakest capacitor.
The RC time constant is τ = R × C, giving the time in seconds for a capacitor to charge to about 63.2% of the supply voltage or discharge to 36.8% of its initial value through a resistor.
With R = 1000 Ω and C = 1 µF, τ = 1000 × 1×10⁻⁶ = 0.001 s (1 ms). After five time constants (5τ = 5 ms here) the capacitor is roughly 99.3% charged and treated as fully settled.
As Khan Academy explains, this exponential response governs timing, filtering, and oscillator circuits, so τ is a core design parameter in analog electronics.
A charged capacitor stores energy in its electric field according to E = ½ × C × V², measured in joules. For a 1000 µF (0.001 F) capacitor charged to 12 V, E = ½ × 0.001 × 12² = ½ × 0.001 × 144 = 0.072 J.
Because energy scales with the square of voltage, doubling the voltage quadruples the stored energy. The related stored charge is Q = C × V, so the same capacitor at 12 V holds Q = 0.001 × 12 = 0.012 C.
Encyclopaedia Britannica notes this squared-voltage relationship is why high-voltage capacitors remain hazardous even at modest capacitance.
A dielectric is the insulating material between capacitor plates, and its relative permittivity εᵣ multiplies the vacuum capacitance directly in C = ε₀ × εᵣ × A / d.
Choosing a high-εᵣ dielectric packs far more capacitance into the same physical volume, which is how a coin-sized ceramic capacitor rivals a much larger air-gap design.
The IEC standardizes dielectric classes (such as C0G/NP0 and X7R) that trade permittivity against temperature stability, as HyperPhysics also discusses.
In an AC circuit a capacitor opposes changing voltage with capacitive reactance Xc = 1 / (2πfC), measured in ohms, where f is the frequency in hertz and C is the capacitance in farads.
Reactance falls as frequency or capacitance rises, so a capacitor blocks low-frequency and DC signals while passing high-frequency ones. For a 1 µF capacitor at 60 Hz, Xc = 1 / (2π × 60 × 1×10⁻⁶) ≈ 2653 Ω.
As IEEE circuit references explain, this frequency dependence makes capacitors central to filters, coupling networks, and power-factor correction in AC power systems.
Capacitance calculations underpin most electronic design decisions. Engineers size smoothing capacitors to limit power-supply ripple, choose coupling capacitors that pass audio while blocking DC bias, and set RC time constants for oscillators, debounce circuits, and 555-timer stages.
Power engineers add parallel capacitor banks for power-factor correction, while photographers rely on high-energy capacitors that dump stored joules into a xenon flash tube. Automotive and renewable systems use large electrolytic and supercapacitor arrays for energy buffering.
As Encyclopaedia Britannica and Khan Academy both illustrate, the same core formulas scale from picofarad RF tuning to farad-scale energy storage.
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All formulas verified against official standards.