Toroid Inductance Calculator

The concept of a toroid and its inductance is an important aspect of Electromagnetism, a subset of Physics. A toroid is a coil of wire in the shape of a doughnut and has a magnetic field within the doughnut's hole. Inductance is the property of an electrical conductor to create a voltage when the current flowing through it changes. This tutorial explains how to calculate the inductance of a toroid given parameters such as the number of turns, the height, inner radius, outer radius, and the permeability of free space.

Toroid Inductance Calculator
Toroid Inductance Calculator Results
Inductance (L) = H

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Example Formula

The inductance of a toroid can be calculated using the following formula:

L = (μ0 × μr × N2 × π × r2) / (2 × π × r)


  1. L represents the inductance of the toroid.
  2. μ0 represents the permeability of free space (4π × 10-7 T m/A).
  3. μr is the relative permeability of the material.
  4. N is the number of turns of the wire.
  5. r is the average radius of the toroid.

Who wrote/refined the formula

The formula for inductance of a toroid is derived from Maxwell's equations, a set of four differential equations formulated by James Clerk Maxwell in 1861-62. The equations provide a mathematical model for electric, optical, and radio technologies, such as power generation, electric motors, wireless communication, lenses, radar, etc.

Real Life Application

Toroid inductors are widely used in electronic circuits, particularly in applications like power supplies, signal processing, and telecommunications. Their donut shape makes them very effective at reducing magnetic interference, thus improving the quality and efficiency of electrical devices.

Key individuals in the discipline

James Clerk Maxwell, a Scottish scientist, is the key individual associated with this concept. His formulation of the classical theory of electromagnetic radiation brought together for the first time electricity, magnetism, and light as different manifestations of the same phenomenon.

Interesting Facts

  1. Maxwell's equations, which lead to the formulation for toroid inductance, have been called the "second great unification in physics" after the first one realised by Isaac Newton.
  2. Inductors, including toroids, are essential in every electronic device you use daily. From your smartphone to the satellite systems in space, they all use inductors to manage electrical energy efficiently.
  3. One of the advantages of toroid inductors is that they have almost no magnetic field leakage. This feature makes them highly efficient and prevents them from generating noise in other parts of the circuit.


Understanding toroid inductance is critical for the development and enhancement of electronic circuits and systems. Its implications extend from daily-use electronic devices to complex systems like power supplies and signal processors. As such, the understanding and calculation of toroid inductance continue to be a vital part of Physics, particularly in the field of Electromagnetism.

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