Electrical charge storage
What is capacitance?
Capacitance describes the ability of a capacitor or electrical system to store electric charge when a voltage is applied.
A larger capacitance means more charge can be stored at the same voltage. Capacitance depends on the conductor geometry, separation, and dielectric material.
Main capacitor equation
Capacitance formula
CapacitanceC = Q ÷ V
- C is capacitance in farads.
- Q is stored electric charge in coulombs.
- V is voltage in volts.
The same relationship can be rearranged as Q = CV to calculate charge and V = Q/C to calculate voltage.
Worked example
Calculate capacitance from charge and voltage
Suppose a capacitor stores 0.000024 C of charge at a potential difference of 12 V.
- Use C = Q ÷ V.
- Substitute Q = 0.000024 C and V = 12 V.
- C = 0.000024 ÷ 12.
- The capacitance is 0.000002 F, or 2 μF.
Farad conversions
Capacitance units
- 1 farad (F) = 1 coulomb per volt.
- 1 millifarad (mF) = 10⁻³ F.
- 1 microfarad (μF) = 10⁻⁶ F.
- 1 nanofarad (nF) = 10⁻⁹ F.
- 1 picofarad (pF) = 10⁻¹² F.
Convert capacitance to farads before entering it. For example, 470 nF is entered as 0.00000047 F.
Practical applications
Where capacitance is used
- Energy storage in electronic circuits.
- Filtering and smoothing power supplies.
- Timing circuits and oscillators.
- Signal coupling and noise suppression.
- Sensors and touch-sensitive devices.
Model limitations
Assumptions and limitations
- Values are treated as positive magnitudes.
- Capacitance is assumed to remain constant during the calculation.
- Leakage current and dielectric loss are not included.
- Frequency-dependent capacitance is not modelled.
- This calculator does not calculate capacitor energy or RC time constants.
Common questions
Capacitance calculator FAQ
What formula does the capacitance calculator use?
It uses C = Q/V, where capacitance equals stored charge divided by voltage. The equation can also be rearranged as Q = CV and V = Q/C.
What is the SI unit of capacitance?
The SI unit of capacitance is the farad, written F. One farad equals one coulomb of charge stored per volt.
How do I calculate charge stored by a capacitor?
Multiply capacitance by voltage using Q = CV. Use capacitance in farads and voltage in volts to obtain charge in coulombs.
How do I convert microfarads to farads?
Multiply microfarads by 10⁻⁶. For example, 2 microfarads equals 0.000002 farads.
Does this calculator determine capacitor energy?
No. This calculator covers capacitance, charge, and voltage. Capacitor energy requires a separate equation such as U = 1/2 CV².