Where is the energy stored?
In the magnetic field of the inductor. When the current drops, this energy is released — which is why inductors resist current changes and produce voltage spikes when switched off.
Inductor Energy Calculator
E = ½LI²
Calculate energy stored in an inductor from inductance and current. E = ½LI².
Calculate
Enter values above to calculate
How it calculates
1
Read L in henries (H) and I in amperes (A)
2
Compute: E = ½ × L × I²
3
Result in joules
Formula
E = ½LI²
Variable Table
| Symbol | Quantity | SI Unit |
|---|---|---|
| E | Stored energy | J |
| L | Inductance | H |
| I | Current | A |
How to Use This Calculator
This inductor 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 = ½LI² 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
Find energy in a 10 mH inductor carrying 2 A.
Step 1: E = ½LI²
Step 2: E = ½ × 0.01 × 4
Answer: E = 0.02 J = 20 mJ
Common Mistakes
- Compare with capacitor: E = ½CV². Both store energy proportional to the square of the field quantity
- Inductance is in henries (H), not mH — convert millihenries first
- Inductor energy is stored in the magnetic field; capacitor energy in the electric field
Related
Frequently Asked Questions
What is inductance?
A measure of how strongly a coil opposes changes in current. SI unit: henry (H) = V·s/A.