A farad (F) is the SI unit of capacitance. One farad means the capacitor stores one coulomb of charge per volt applied. One farad is enormous; most practical capacitors are measured in microfarads, nanofarads, or picofarads.

What is a dielectric material?

A dielectric is an insulating material placed between capacitor plates that increases capacitance by reducing the electric field strength. Common dielectrics include air, paper, ceramic, mica, and various plastics.

How do capacitors in series differ from parallel?

In parallel, capacitances add directly (C_total = C1 + C2). In series, reciprocals add (1/C_total = 1/C1 + 1/C2), giving a smaller total capacitance. Series is used for voltage division, parallel for increasing storage.

What is the time constant of a capacitor?

The time constant (tau = R × C) is the time for a capacitor to charge to about 63% of the supply voltage through a resistor. After 5 time constants, the capacitor is considered fully charged (over 99%).

Can capacitors replace batteries?

Supercapacitors can replace batteries in some applications. They charge in seconds and last millions of cycles, but store less energy per unit weight. They excel in applications needing quick bursts of power like regenerative braking.

Capacitance Calculator

Calculate charge, voltage, or capacitance (Q = CV)

Capacitance (Q = CV)

Enter any two to find the third

Capacitance (F)

Voltage (V)

Charge (C)

Formula

Q = C x V

What Is Capacitance?

Capacitance is a measure of a capacitor's ability to store electrical charge. When a voltage is applied across a capacitor, charge accumulates on its plates. The capacitance (C) tells you how much charge (Q) is stored per unit of voltage (V). A higher capacitance means more charge can be stored at the same voltage.

Capacitors are everywhere in electronics: smoothing power supplies, filtering signals, storing energy in camera flashes, setting timing in oscillator circuits, and coupling AC signals between amplifier stages. Understanding capacitance calculations helps you select the right capacitor for your circuit and predict how it will behave.

How to Use This Calculator

Select which quantity you want to solve for: Capacitance (C), Charge (Q), or Voltage (V).
Enter the two known values with their units (farads, coulombs, or volts).
Click Calculate to instantly see the unknown value.
Use Reset to clear the fields and start a new calculation.

Formula & Explanation

C = Q / V
Q = C × V
V = Q / C

C = Capacitance in farads (F), Q = Electric charge in coulombs (C), V = Voltage in volts (V). Practical capacitors range from picofarads (pF, 10⁻¹²) for RF circuits to farads for supercapacitors.

Worked Examples

Example 1 — Find Charge

A 100 µF capacitor is charged to 12 V. Q = C × V = 100×10⁻⁶ × 12 = 0.0012 C = 1.2 mC.

Example 2 — Find Voltage

A 470 µF capacitor holds 94 mC of charge. V = Q / C = 0.094 / 470×10⁻⁶ = 200 V.

Example 3 — Find Capacitance

A capacitor stores 50 µC at 25 V. C = Q / V = 50×10⁻⁶ / 25 = 2 µF.

Frequently Asked Questions

What are the common units for capacitance?▾

Capacitance is measured in farads (F), but most practical capacitors are in microfarads (µF = 10⁻⁶ F), nanofarads (nF = 10⁻⁹ F), or picofarads (pF = 10⁻¹² F). Supercapacitors reach farads and even kilofarads.

How does capacitance affect charging time?▾

A larger capacitor takes longer to charge and discharge through a given resistance. The RC time constant (τ = R × C) gives the time for the voltage to reach about 63% of its final value. After 5τ, the capacitor is considered fully charged.

What happens when capacitors are connected in parallel?▾

Capacitors in parallel add directly: Ctotal = C1 + C2 + C3. Their voltages are equal, and total charge is the sum of individual charges. Parallel connection increases total capacitance.

What happens when capacitors are connected in series?▾

For capacitors in series, 1/Ctotal = 1/C1 + 1/C2 + ... The total capacitance is less than any individual capacitor. Series connection increases the effective voltage rating.

What is the energy stored in a capacitor?▾

The energy stored is E = ½ × C × V². A 1000 µF capacitor charged to 10 V stores E = 0.5 × 0.001 × 100 = 0.05 joules = 50 mJ. This energy releases instantly when discharged, which is why camera flashes work.