What is capacitance?
The charge stored per unit voltage: C = Q/V. SI unit: farad (F) = C/V. Most capacitors are μF or pF.
Capacitor Energy Calculator
E = ½CV²
Calculate energy stored in a capacitor from capacitance and voltage. E = ½CV².
Calculate
Enter values above to calculate
How it calculates
1
E = ½ × C × V²
2
C in farads, V in volts
3
Result in joules
Formula
E = ½CV²
Variable Table
| Symbol | Quantity | SI Unit |
|---|---|---|
| E | Stored energy | J |
| C | Capacitance | F |
| V | Voltage | V |
| Q | Charge = CV | C |
How to Use This Calculator
This capacitor energy calculator is built for quick physics checks and worked-problem review. Enter values in the units shown beside each input, then compare the result with the formula and variable table before using it in a longer solution. The calculator does the arithmetic, but the physics still depends on choosing a model that matches the situation.
Start by identifying the system, the known quantities, and the quantity you want to find. If a value is given in a non-SI unit, convert it before substitution. A correct numerical answer with mixed units can still be physically wrong, especially when squared units, inverse seconds, charges, temperatures, or distances are involved.
Assumptions and Limits
The formula E = ½CV² is a model, not a universal description of every possible case. It assumes the quantities in the variable table are the relevant quantities for the problem and that hidden effects are either negligible or already included in the inputs. If friction, drag, relativistic speeds, changing fields, non-constant temperature, or geometry-specific effects matter, check whether a more complete model is needed.
Use the result as a magnitude and units check. Ask whether the answer has the right sign, whether it grows or shrinks when an input changes, and whether the limiting cases make sense. Setting an input to zero, doubling a quantity, or using a very large value is often enough to catch a formula choice or unit mistake before it reaches a final answer.
Worked Example
A 1 mF capacitor charged to 12 V. Find stored energy.
Step 1: E = ½CV²
Step 2: E = ½ × 0.001 × 144
Answer: E = 0.072 J = 72 mJ
Common Mistakes
- Convert μF and mF to farads (1 μF = 10⁻⁶ F)
- Energy ∝ V² — doubling voltage quadruples stored energy
- Capacitor energy is in the electric field; inductor energy is in the magnetic field
Related
Frequently Asked Questions
Where is the energy stored?
In the electric field between the capacitor plates. It can discharge rapidly — the basis of camera flashes and defibrillators.