Inductance Calculator
Calculate the inductance of solenoids, toroids, and straight wires. Enter your coil dimensions, number of turns, and core material to get accurate inductance values in henries (H), millihenries (mH), and microhenries (µH). Perfect for electronics design, RF circuits, and power supply applications.
What Is Inductance?
Inductance is the property of an electrical conductor that opposes changes in current flow. When current flows through a coil, it creates a magnetic field. Any change in current induces a voltage (electromotive force) that opposes the change — this is known as self-inductance. The unit of inductance is the henry (H).
The inductance of a coil depends on several factors:
- Number of turns (N): Inductance is proportional to N².
- Core material: Higher permeability (µr) increases inductance.
- Coil geometry: The shape and dimensions of the coil affect the magnetic flux path.
- Cross-sectional area: Larger area increases inductance.
How Does the Inductance Calculator Work?
The calculator uses standard formulas for each geometry:
Solenoid: L = (µ₀ × µr × N² × A) / l
Where: A = π × r² (cross-sectional area), l = length, µ₀ = 4π × 10⁻⁷ H/m
Toroid: L = (µ₀ × µr × N² × A) / (2π × R)
Where: R = major radius, A = π × r² (minor cross-section)
Straight Wire: L ≈ 2×10⁻⁷ × L × (ln(2L/r) − 0.75)
Where: L = wire length, r = wire radius
The calculator also calculates the reactance at 60 Hz using XL = 2π × f × L, where f = 60 Hz.
Why Use This Inductance Calculator?
- Three Geometries: Supports solenoids, toroids, and straight wires.
- Core Materials: Choose from air, ferrite, iron, mu-metal, nickel, steel, or custom permeability.
- Unit Flexibility: Switch between metric (meters) and imperial (inches, feet).
- Reactance Calculation: Automatically calculates reactance at 60 Hz.
- Free & Private: No registration, no data storage.
❓ Inductance Calculator FAQ
What is inductance?
Inductance is the property of an electrical conductor that opposes changes in current flow. It is measured in henries (H). A coil with higher inductance stores more magnetic energy for a given current.
What is the unit of inductance?
The SI unit of inductance is the henry (H). Common subunits are millihenry (mH = 10⁻³ H) and microhenry (µH = 10⁻⁶ H).
What is the formula for solenoid inductance?
For a solenoid: L = (µ₀ × µr × N² × A) / l, where µ₀ = 4π × 10⁻⁷ H/m, µr is relative permeability, N is the number of turns, A is cross-sectional area, and l is length.
What is the formula for toroid inductance?
For a toroid: L = (µ₀ × µr × N² × A) / (2π × R), where R is the major radius and A is the cross-sectional area of the torus.
What is the formula for straight wire inductance?
For a straight wire: L ≈ 2×10⁻⁷ × L × (ln(2L/r) − 0.75), where L is the wire length and r is the wire radius.
What is relative permeability (µr)?
Relative permeability is the ratio of the permeability of a material to the permeability of free space (µ₀). Air has µr = 1. Ferrite can have µr up to 2,000 or more.
What is the permeability of free space (µ₀)?
µ₀ = 4π × 10⁻⁷ H/m ≈ 1.2566 × 10⁻⁶ H/m. It is the magnetic constant.
How does the number of turns affect inductance?
Inductance is proportional to the square of the number of turns (L ∝ N²). Doubling the number of turns quadruples the inductance.
What is inductive reactance?
Inductive reactance (XL) is the opposition to AC current flow caused by inductance. It is calculated as XL = 2π × f × L, where f is the frequency in hertz.
How does core material affect inductance?
Core materials with higher permeability (µr) increase inductance. For example, a ferrite core (µr ≈ 2000) will produce 2000 times more inductance than an air core of the same geometry.
What is the difference between a solenoid and a toroid?
A solenoid is a cylindrical coil with a straight axis. A toroid is a coil wound in a ring shape (doughnut). Toroids have better magnetic field confinement and less electromagnetic interference.
Can I use this calculator for air-core inductors?
Yes. Select "Air" as the core material (µr = 1.000). This is the default setting for air-core inductors used in high-frequency applications.
What is the inductance of a straight wire?
A straight wire has a small but measurable inductance. For a 1-meter wire with 0.5 mm radius, the inductance is approximately 1.3 µH. This calculator uses the standard formula for straight wire inductance.
What is the difference between self-inductance and mutual inductance?
Self-inductance is the property of a coil that opposes changes in its own current. Mutual inductance is the property of a coil that induces voltage in a nearby coil due to changing current.
How does frequency affect inductive reactance?
Inductive reactance increases linearly with frequency (XL = 2πfL). Higher frequencies result in higher reactance, which means the inductor offers more opposition to AC current.
What is the difference between inductance and capacitance?
Inductance stores energy in a magnetic field and opposes changes in current. Capacitance stores energy in an electric field and opposes changes in voltage. They are complementary components in electrical circuits.
How do I measure inductance in a circuit?
Inductance can be measured using an LCR meter, an impedance analyzer, or by measuring the resonant frequency of an LC circuit. For rough estimates, you can use the formulas in this calculator.
What is the typical inductance of a power inductor?
Power inductors range from a few microhenries (µH) for high-frequency switching converters to several millihenries (mH) for low-frequency power supplies. This calculator can help you estimate the inductance for your design.