Capacitance to Charge Calculator

Q: How do I calculate charge from capacitance?

Multiply capacitance in farads by voltage: Q = C × V. For 47 μF at 9 V: 47 × 10⁻⁶ × 9 = 0.000423 C = 423 μC.

Q: How much energy does a capacitor store?

E = ½ × C × V². A 1,000 μF capacitor at 25 V stores ½ × 0.001 × 625 = 0.3125 J.

Q: What is 1 farad in coulombs?

A 1 farad capacitor holds 1 coulomb of charge for every volt across it. At 5 V it holds 5 C.

Q: Why is stored energy ½QV and not QV?

Because the voltage rises from zero as the capacitor charges, so on average each bit of charge was moved through half the final voltage. The other half of the energy supplied is lost as heat in the charging resistance.

Q: Is it safe to touch a charged capacitor?

Not necessarily. Large capacitors in power supplies, microwaves and flash units can hold dangerous energy after the power is off. Discharge them safely through a suitable resistor before handling.

Calculate electric charge from capacitance and voltage with Q = C × V, in pF, nF, μF, mF or F. Also shows stored energy, E = ½CV².

🔋 CAPACITANCE

🔌 VOLTAGE

ELECTRIC CHARGE

0.0012 C

COULOMBS

1.200e-3 C

FORMULA

Q = C × V

ENERGY (J)

0.0072 J

💡 How to Calculate Charge from Capacitance

To find the charge on a capacitor, multiply its capacitance in farads by the voltage across it: Q = C × V. Convert the capacitance to farads first (1 μF = 10⁻⁶ F). The charge comes out in coulombs.

Charge and energy formulas

Q = C × V · E = ½ × C × V² = ½ × Q × V

Q = charge in coulombs, C = capacitance in farads, V = voltage in volts, E = stored energy in joules
Example: 100 μF at 12 V → Q = 100 × 10⁻⁶ × 12 = 1.2 mC; E = ½ × 100 × 10⁻⁶ × 12² = 7.2 mJ

Capacitance unit prefixes

Unit	Farads
1 pF (picofarad)	10⁻¹² F
1 nF (nanofarad)	10⁻⁹ F
1 μF (microfarad)	10⁻⁶ F
1 mF (millifarad)	10⁻³ F
1 F (farad)	1 F

Worked examples

Power-supply filter capacitor: 4,700 μF at 50 V holds 235 mC and stores 5.875 J, enough to give a real shock, which is why such capacitors must be discharged before servicing.
Decoupling capacitor: 100 nF at 12 V holds just 1.2 μC.
Supercapacitor: 3,000 F at 2.7 V holds 8,100 C and stores 10,935 J (about 3.04 Wh).

Charge and energy table

Capacitance	Voltage (V)	Charge (Q)	Stored energy (E)
10 pF	5	50 pC	125 pJ
1 nF	5	5 nC	12.5 nJ
100 nF	12	1.2 μC	7.2 μJ
10 μF	5	50 μC	125 μJ
100 μF	12	1.2 mC	7.2 mJ
1,000 μF	25	25 mC	312.5 mJ
4,700 μF	50	235 mC	5.875 J
1 F	5.5	5.5 C	15.125 J
3,000 F	2.7	8,100 C	10,935 J

How fast a capacitor charges

Charging through a resistor follows the time constant τ = R × C (seconds, with R in ohms and C in farads). After one time constant the capacitor reaches about 63.2% of the supply voltage, and after five time constants about 99.3%, which is usually treated as fully charged.

Practical notes

Respect the voltage rating. Exceeding a capacitor's rated voltage can damage it or cause electrolytic capacitors to fail violently.
Tolerance matters. Electrolytic capacitors often have tolerances of ±20%, so real charge can differ noticeably from the calculated value.

Related conversions: volts to joules · joules to volts · watts to joules

Q = C × V. 100 μF at 12 V holds 1.2 mC of charge and stores 7.2 mJ of energy.