Inductor Energy Storage Calculator
Are you wondering what this inductor energy storage calculator can do? Well, it estimates the energy stored in an inductor when an electric current is passing through it. We also provide the equation for the magnetic energy in the solenoid and explain where this energy equation comes from. Further in the text, you'll also find a useful piece of information about how we can use this phenomenon in practice. The calculator supports both the metric (SI) and American (imperial) unit systems.
🙋 You can always estimate any coil's inductance with a solenoid inductance calculator.
What is the energy stored in an inductor
A solenoid is one of the most common electronic components. Solenoids have the ability to generate magnetic fields, and the ease with which the solenoid can create this field is known as its inductance. It's important to understand that this magnetic field is present only if there is a current flow through the coil.
Interestingly, the magnetic field accumulates a portion of energy, which can be released (or absorbed) whenever the value of the current changes. That's the reason why an inductor is a source of impedance in AC circuits.
Magnetic energy stored in a coil formula
Assuming we have an electrical circuit containing a power source and a solenoid of inductance L, we can write the equation of magnetic energy, E, stored in the inductor as:
E = ½ × L × I²
where I is the current flowing through the wire. In other words, we can say that this energy is equal to the work done by the power source to create such a magnetic field.
As we can see, the energy stored in an inductor depends on the current to the second power. This tells us that the solenoid prevents a sudden current surge in the circuit, and that's the reason why we can see a spark when unplugging some electronic devices.
Where:
- L — the inductance of the coil, measured in henries (H). The calculator also accepts millihenries (mH), microhenries (µH), and nanohenries (nH).
- I — the current flowing through the inductor, measured in amperes (A), milliamperes (mA), or microamperes (µA).
- E — the magnetic energy stored in the inductor. In metric units it is given in joules (J); in American units we also show it in foot-pounds (ft·lbf) and BTU.
How to use the inductor energy storage calculator?
Let's say we have a circuit containing a power source and a coil of inductance L = 20 µH. We are looking for the energy stored in the inductor when we pass a direct current of I = 300 mA through the system.
In case you don't want to mess up with your units, let's write all the values using scientific notation:
L = 2×10⁻⁵ H, I = 3×10⁻¹ A
Use the formula for magnetic energy in the solenoid:
E = ½ × 2×10⁻⁵ H × (3×10⁻¹ A)² = 9×10⁻⁷ J
We can also write the energy stored in the inductor as E = 0.9 µJ or 900 nJ. You can always use this inductor energy storage calculator to make sure your result is correct!
Sometimes we may need to have more energy stored for our application. One thing we can do is to increase the inductance by adding a material with high permeability, like ferromagnetic cores.
Applications of magnetic energy storage
The ability of inductors to store energy in a magnetic field is used in many practical devices and circuits:
- Switching power supplies and DC-DC converters — inductors store energy during one part of the switching cycle and release it during another, allowing voltage to be stepped up (boost) or down (buck) efficiently.
- Filters and chokes — because an inductor opposes sudden changes in current, it smooths out ripple and blocks high-frequency noise.
- Energy recovery — the stored magnetic energy is what produces the spark or voltage spike you sometimes see when a current-carrying coil is suddenly disconnected.
- Superconducting magnetic energy storage (SMES) — large superconducting coils store substantial amounts of energy with almost no resistive loss for grid stabilization.
Unit Systems
Metric (SI)
- Inductance L: H, mH, µH, nH (henries and submultiples)
- Current I: A, mA, µA (amperes and submultiples)
- Energy result: J (joules), also shown in mJ, µJ, nJ, kJ, Wh, cal, BTU, ft·lbf
American (Imperial)
- Inductance and current use the same universal units (henries and amperes), since they are SI units used worldwide.
- Energy result is highlighted in ft·lbf (foot-pounds) and also shown in BTU, alongside the full metric conversion table.
Frequently Asked Questions
What is the energy stored in an inductor?
It is the energy held in the magnetic field that an inductor creates when current flows through it. It equals E = ½ × L × I², where L is the inductance and I is the current. This energy is released back into the circuit when the current decreases.
Why does the energy depend on the current squared?
Because the formula E = ½ × L × I² contains I². This means doubling the current quadruples the stored energy. It also explains why an inductor resists sudden changes in current and why disconnecting it can cause a voltage spike or spark.
How can I store more energy in an inductor?
You can increase either the current or the inductance. Inductance can be raised by adding more turns to the coil or by inserting a high-permeability core, such as a ferromagnetic (iron or ferrite) core.
What units are used for inductance and current?
Inductance is measured in henries (H); practical components are often in millihenries (mH), microhenries (µH), or nanohenries (nH). Current is measured in amperes (A), or milliamperes (mA) and microamperes (µA) for small signals. The calculator converts all of these to SI base units automatically.
Is the stored energy ever negative?
No. Since the current is squared in the formula, the stored magnetic energy is always zero or positive, regardless of the direction of the current.