Quick answer
Capacitance is stored charge divided by voltage: C = Q ÷ V. A charge of 100 µC at 5 V gives 20 µF.
Enter the charge and the voltage. The calculator returns capacitance.
Related tools: Inductance Calculator: Inductance of a long air- or core-filled solenoid.
How to use the Capacitance Calculator
- Enter charge (µC) (above 0).
- Enter voltage (V) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Charge | A number, in µC | > 0 |
| Voltage | A number, in V | > 0 |
Formula and method
Formula
C = Q ÷ V
IEEE-754 double precision; shown to the decimals indicated.
Charge in microcoulombs gives capacitance in microfarads.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Charge = 100; Voltage = 5.
| Result | Value |
|---|---|
| Capacitance | 20 µF |
Example 2
Inputs: Charge = 2.2; Voltage = 12.
| Result | Value |
|---|---|
| Capacitance | 0.183333 µF |
Example 3
Inputs: Charge = 47; Voltage = 25.
| Result | Value |
|---|---|
| Capacitance | 1.88 µF |
The first line is the headline result (capacitance). IEEE-754 double precision; shown to the decimals indicated.
Units
One farad is one coulomb per volt, so practical capacitors are measured in microfarads (10⁻⁶ F), nanofarads or picofarads. The energy stored is ½CV²; for 20 µF at 5 V it is 250 µJ.
Related calculation
Capacitors in parallel add (C₁ + C₂) while capacitors in series combine as 1 ÷ (1/C₁ + 1/C₂).
Charge, voltage and stored energy
C = Q ÷ V is the ratio of charge to voltage: 100 µC at 5 V is 20 µF. One farad is one coulomb per volt, and microfarads (10⁻⁶ F) are the usual scale for circuits.
Such a capacitor stores ½ C V² = ½ × 20×10⁻⁶ × 25 = 250 µJ. The page works from measured charge and voltage; physical plate geometry is a separate calculation.
How the result changes with charge
Holding every other input at the first worked example, this table changes only charge. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Charge | Capacitance |
|---|---|
| 50 | 10 µF |
| 100 | 20 µF |
| 200 | 40 µF |
| 400 | 80 µF |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Charge: entering "0" shows "Charge must be greater than 0." beside that field and no result.
- Voltage: entering "0" shows "Voltage must be greater than 0." beside that field and no result.
Choosing between the Capacitance Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Inductance Calculator](/science/inductance-calculator/) | number of turns, core cross-section and coil length | Inductance |
| [Voltage Divider Calculator](/engineering/voltage-divider-calculator/) | input voltage, r1 and r2 | Output voltage |
| [RLC Impedance Calculator](/engineering/rlc-impedance-calculator/) | resistance, inductance and capacitance | Impedance |
| [RMS Voltage Calculator](/engineering/rms-voltage-calculator/) | i know the and voltage | RMS voltage |
| [Parallel Plate Capacitor Calculator](/engineering/parallel-plate-capacitance-calculator/) | plate area, plate separation and relative permittivity εr | Capacitance |
Assumptions and limitations
- Ideal capacitor
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for charge and voltage to confirm this.
Frequently asked questions
What is a farad?
A farad is one coulomb of charge per volt, a very large unit for real capacitors.
How much energy is stored?
Energy is ½CV², which is 250 µJ for 20 µF at 5 V.
Does the voltage rating matter?
Yes, exceeding it damages the part.
How is capacitance found from plate geometry?
For parallel plates C = ε₀εᵣA ÷ d, with plate area A, spacing d and the dielectric constant εᵣ.
What is a microfarad?
One microfarad is 10⁻⁶ farad, a millionth of a farad.
What does the Capacitance Calculator calculate?
Capacitance from charge and voltage. It returns Capacitance.
What formula does the Capacitance Calculator use?
C = Q ÷ V. Charge in microcoulombs gives capacitance in microfarads.
What do I need to enter in the capacitance Calculator?
You enter Charge (µC) and Voltage (V).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Ideal capacitor.
What is an example of a capacitance result?
With charge 100 and voltage 5, the capacitance is 20 µF.
Where does the method come from?
The method follows: OpenStax, University Physics Volume 2 (Rice University): electricity, circuits and thermodynamics: capacitance, C = Q ÷ V.
Related calculators
- Inductance Calculator — Inductance of a long air- or core-filled solenoid.
Sources
- OpenStax, University Physics Volume 2 (Rice University): electricity, circuits and thermodynamics: capacitance, C = Q ÷ V
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.