Toroidal Inductor Calculator

A toroidal inductor is a donut-shaped coil used in power supplies, filters, and audio equipment to store electromagnetic energy efficiently. Enter your core's outer diameter, inner diameter, height, number of turns, relative permeability, and wire diameter into the Toroidal Inductor Calculator to find the inductance of your coil. Secondary outputs include the AL factor (inductance per turn²), wire length required, and mean turn length.

mm

Outer diameter of the toroidal core

mm

Inner diameter of the toroidal core

mm

Height or thickness of the toroidal core

Total number of wire turns around the core

Relative permeability of the core material (use 1 for air core)

mm

Diameter of the wire including insulation

Results

Inductance

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AL Factor

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Wire Length Required

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Mean Turn Length

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Frequently Asked Questions

What is the difference between air core and magnetic core toroidal inductors?

Air core inductors use air (μr = 1) as the core material, providing linear characteristics but lower inductance. Magnetic core inductors use ferrite or iron powder (μr > 1) to significantly increase inductance but may have nonlinear characteristics at high currents.

How do I determine the relative permeability (μr) of my toroidal core?

The relative permeability depends on the core material. Common values: Air = 1, Iron powder = 10-100, Ferrite = 1000-5000. Check the manufacturer's datasheet for exact values, as μr varies with frequency and flux density.

What is the AL factor and how is it used?

The AL factor represents the inductance per turn squared (nH/N²) and is a core-specific parameter. It allows quick calculation of inductance: L = AL × N². Higher AL values mean more inductance for the same number of turns.

How do I calculate the wire length needed for winding?

Wire length equals the number of turns multiplied by the mean turn length. The mean turn length is approximately π times the average of inner and outer diameters: MTL = π × (Do + Di) / 2.

Why are toroidal inductors preferred over other shapes?

Toroidal inductors offer superior magnetic field containment, reducing electromagnetic interference. They provide higher inductance per unit volume, lower leakage inductance, and better coupling between windings compared to solenoid or air-core inductors.

What factors affect the accuracy of toroidal inductor calculations?

Calculation accuracy depends on core material uniformity, frequency of operation, current levels, and winding distribution. At high frequencies, parasitic capacitance and core losses become significant. Temperature also affects permeability.

How do I choose the right wire gauge for my toroidal inductor?

Wire gauge selection depends on current capacity, skin effect at operating frequency, and physical fit within the core window. Use AWG charts for current ratings and ensure the total wire cross-sectional area doesn't exceed 40-60% of the core window area.

Can I stack multiple turns in layers on a toroidal core?

Yes, but layered windings increase leakage inductance and parasitic capacitance. Single-layer windings provide the most accurate inductance calculations. If multiple layers are necessary, distribute turns evenly around the core circumference.