What this calculator does
Capacitance measures how much electric charge a component can store for each volt applied across it. The capacitance formula is C = Q/V: capacitance equals stored charge divided by voltage, and rearranging the same equation solves for charge (Q = CV) or voltage (V = Q/C) whenever the other two quantities are known.
This calculator works from that single relationship in whichever direction you need: enter charge and voltage to find capacitance, capacitance and voltage to find stored charge, or capacitance and charge to find voltage. Capacitance is usually quoted in microfarads (µF) or smaller, so a table below also restates the result in picofarads, nanofarads, microfarads and farads.
The formula
Capacitance, charge and voltage are related by C = Q/V. Choose which one to solve for, enter the other two, and the calculator applies whichever rearrangement of that equation is needed: C = Q/V, Q = CV, or V = Q/C.
| Term | Meaning |
|---|---|
| C | Capacitance, measured in farads (F), or more commonly microfarads (µF), nanofarads (nF) or picofarads (pF) for real components. |
| Q | Electric charge stored, measured in coulombs (C), or microcoulombs (µC) for the small charges typical of everyday capacitors. |
| V | Voltage across the capacitor, measured in volts (V). |
The inputs explained
| Field | What to enter |
|---|---|
| Solve for | Choose which quantity to calculate from the other two. |
| Charge (µC) | The stored charge, in microcoulombs (µC). Only used when charge is known (solving for capacitance or voltage). |
| Capacitance (µF) | The capacitance, in microfarads (µF). Only used when capacitance is known (solving for charge or voltage). |
| Voltage (V) | The voltage across the capacitor, in volts. Only used when voltage is known (solving for capacitance or charge). |
When to use it
Finding the capacitance of an unlabelled or measured component
If a stored charge and the voltage that produced it have been measured directly, C = Q/V gives the capacitance without needing to read a marking on the component itself.
Working out how much charge a capacitor will store
Given a known capacitance and the supply voltage it will be charged to, Q = CV gives the charge stored at full charge, which feeds into further calculations such as stored energy.
Checking a component against its rated voltage
Given a known capacitance and a target stored charge, V = Q/C shows what voltage that requires, which can then be checked against the component's voltage rating.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How capacitance changes with charge at a fixed voltage
A fixed 5 V, across a range of stored charge values.
How capacitance changes with voltage at a fixed charge
A fixed 100 µC of charge, across a range of voltages.
| Voltage | Capacitance |
|---|---|
| 3.3 V | 30.3030303 µF |
| 5 V | 20 µF |
| 9 V | 11.11111111 µF |
| 12 V | 8.33333333 µF |
| 24 V | 4.16666667 µF |
| 48 V | 2.08333333 µF |
Questions
What is the formula for capacitance?
C = Q/V, capacitance equals charge divided by voltage. The same equation rearranges to Q = CV to find charge, or V = Q/C to find voltage, whenever the other two quantities are known.
How do I calculate capacitance from charge and voltage?
Divide the charge by the voltage. For example, a capacitor storing 100 microcoulombs at 5 volts has a capacitance of 20 microfarads (100 µC ÷ 5 V = 20 µF).
What units is capacitance measured in?
The base SI unit is the farad (F), but a farad is an enormous amount of capacitance, so real components are almost always specified in microfarads (µF, one millionth of a farad), nanofarads (nF, one billionth) or picofarads (pF, one trillionth).
Does capacitance depend on the voltage applied?
For an ideal capacitor, no: capacitance is a fixed physical property of the component (set by its plate area, spacing and the dielectric between them), and C = Q/V holds at any voltage within the component's rating. Real components can vary slightly with voltage and temperature, but that is a second-order effect, not the basic relationship.
To see the energy stored alongside the charge at a known capacitance and voltage, use the capacitor charge and energy calculator. For how a capacitor charges and discharges through a resistor over time, see the RC circuit calculator.