Capacitor Energy CalculatorFree online other calculator — instant results, no sign-up
Calculate stored energy from capacitance and voltage.
Sign in to save results and favorites.
About the Capacitor Energy Calculator
The Capacitor Energy Calculator calculates the energy stored in a capacitor from its capacitance in microfarads (µF) and the voltage across it in volts (V). It converts capacitance to farads and applies the capacitor energy equation to return energy in joules. With the default inputs of 1000 µF and 12 V, the stored energy is 0.072 J.
- Capacitance (µF)
- The capacitor's capacitance, entered in microfarads (µF), where 1 µF equals 0.000001 farad.
- Voltage (V)
- The voltage across the capacitor's terminals, entered in volts (V), rather than its maximum rated voltage unless that is the actual applied voltage.
Formula and method
E = (1/2) C V², where C = C_µF × 10⁻⁶; for the defaults, E = (1/2) × (1000 × 10⁻⁶) × 12² = 0.072 J.
- EStored electrical energy in joules (J).
- CCapacitance in farads (F), after converting the input from microfarads.
- C_µFThe numerical capacitance input in microfarads (µF).
- VVoltage across the capacitor in volts (V).
Convert the capacitance from microfarads to farads by multiplying by 10⁻⁶, square the voltage, then multiply those values by one-half. For 1000 µF and 12 V, the converted capacitance is 0.001 F and the squared voltage is 144 V², giving E = 0.5 × 0.001 × 144 = 0.072 J.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Capacitance1000 µF
- Voltage12 V
Results
- Result0.072 J
How to use the Capacitor Energy Calculator
- 1Enter the capacitance in the Capacitance (µF) field; use 1000 for the default example.
- 2Enter the voltage across the capacitor in the Voltage (V) field; use 12 for the default example.
- 3Run the calculation using the entered values.
- 4Read the energy result in joules: the default inputs produce 0.072 J.
Reading your result
The Result row reports the capacitor's total stored electrical energy in joules. For 1000 µF at 12 V, Result = 0.072 J. This is stored energy, not power or discharge duration; the energy delivered to a load depends on the discharge circuit and losses.
Limitations
The equation assumes an ideal capacitor with constant capacitance. Real capacitance can vary with voltage, temperature, frequency, and manufacturing tolerance; leakage and equivalent series resistance also affect practical performance. The calculator does not model discharge time, peak current, breakdown, or usable energy between two nonzero voltages. Use nonnegative capacitance and observe the capacitor's voltage rating and polarity requirements. A stored-energy result alone does not establish whether a capacitor is safe to handle.
Common questions
Why must capacitance in µF be converted before calculating energy?+
The equation E = (1/2) C V² gives joules when C is in farads and V is in volts. The default 1000 µF therefore becomes 0.001 F; using 1000 directly as farads would overstate the energy by a factor of one million.
Should I enter the capacitor's rated voltage or its actual voltage?+
Enter the actual voltage across the capacitor. Its rated voltage is an operating limit, not necessarily its present voltage, so using the rating can overestimate the stored energy.
How do capacitance and voltage affect stored energy?+
Stored energy is directly proportional to capacitance and proportional to voltage squared. At constant voltage, doubling capacitance doubles energy; at constant capacitance, doubling voltage quadruples energy, provided the capacitor remains within its ratings.
Does the 0.072 J result tell me how long the capacitor can power a load?+
No. For the default 1000 µF and 12 V, 0.072 J is the initial stored energy. Runtime also requires the load's power demand, the lowest usable voltage, and circuit losses, because the capacitor's voltage falls as it discharges.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
You might also like
IP Subnet Calculator
Network, broadcast and host range of an IPv4 subnet.
Password Generator
Create a strong random password.
Voltage Drop Calculator
Voltage drop on a copper conductor.
GDP Calculator
GDP by the expenditure approach.
Horsepower Calculator
Horsepower from torque and RPM.
Engine Horsepower Calculator
Estimate horsepower from weight and quarter-mile time.
Results are estimates for informational purposes and are not financial, medical or legal advice.