Inductance Calculator

The Inductance Calculator computes coil inductance for 5 geometries — single-layer solenoid, multi-layer solenoid, toroidal coil, flat spiral, and mutual inductance — using Wheeler's formula with Nagaoka correction. Includes wire parameter estimation, impedance calculator, SVG coil cross-section diagram, and self-resonant frequency. Free, no signup required.

Coil Geometry

Presets

Radius (mm)

Coil Length (mm)

Number of Turns

Wire Gauge (AWG)

Frequency (Hz)

Results

Inductance

17.86 µH

Wire Length

1.51 m

DC Resistance

0.5104 Ω

Copper Weight

0.69 g

Self-Resonant Frequency

37.66 MHz

Inductive Reactance (XL)

1121.93 Ω

Impedance at Frequency

1121.93 Ω

Q Factor

2197.9

Coil Cross-Section

AWG Wire Reference

Gauge	Diameter	Resistance/m	Max Current
AWG 10	2.588 mm	0.0033 Ω/m	33 A
AWG 12	2.053 mm	0.0052 Ω/m	23 A
AWG 14	1.628 mm	0.0083 Ω/m	17 A
AWG 16	1.291 mm	0.0132 Ω/m	13 A
AWG 18	1.024 mm	0.0209 Ω/m	10 A
AWG 20	0.812 mm	0.0333 Ω/m	7.5 A
AWG 22	0.644 mm	0.0530 Ω/m	5 A
AWG 24	0.511 mm	0.0842 Ω/m	3.5 A
AWG 26	0.405 mm	0.1339 Ω/m	2.2 A
AWG 28	0.321 mm	0.2128 Ω/m	1.4 A
AWG 30	0.255 mm	0.3385 Ω/m	0.86 A
AWG 32	0.202 mm	0.5384 Ω/m	0.53 A
AWG 34	0.160 mm	0.8560 Ω/m	0.36 A
AWG 36	0.127 mm	1.361 Ω/m	0.22 A
AWG 38	0.101 mm	2.164 Ω/m	0.14 A
AWG 40	0.080 mm	3.441 Ω/m	0.09 A

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What is an Inductance Calculator?

An inductance calculator determines the inductance (in Henries) of various coil configurations using electromagnetic theory. For a single-layer solenoid, it uses Wheeler's approximation: L = (R²N²)/(9R+10l) in microhenries. For toroids, L = µ₀N²h·ln(R₂/R₁)/(2π). This calculator supports 5 geometries with wire parameter estimation (length, resistance, weight), impedance at frequency (XL = 2πfL), and self-resonant frequency calculation — providing a complete coil design workflow in one tool.

How to Use This Calculator

Select a coil geometry: single-layer, multi-layer, toroidal, flat spiral, or mutual inductance
Enter dimensions (radius, length, turns) or choose a preset for common applications
Optionally select wire gauge (AWG) for resistance and weight calculation
View inductance result with wire parameters and impedance at your operating frequency
Check the self-resonant frequency to ensure your coil operates below it

Frequently Asked Questions

How accurate is Wheeler's formula for inductance?

Wheeler's formula is accurate to within 1% for single-layer solenoids when the coil length is comparable to or greater than the radius. For short coils (length < radius), the Nagaoka correction factor improves accuracy. This calculator applies the correction automatically.

What is self-resonant frequency and why does it matter?

Self-resonant frequency (SRF) is where the coil's parasitic capacitance resonates with its inductance: f_SRF = 1/(2π√LC). Above the SRF, the coil behaves as a capacitor rather than an inductor. Always design your coil to operate well below its SRF.

How do I choose the right wire gauge for my coil?

Wire gauge affects resistance (thinner = more resistance), current capacity, and physical size. For power inductors, use AWG 14-18 for low resistance. For RF coils, AWG 20-26 is common. For signal-level applications, AWG 28-36 works well. The AWG reference table in this calculator shows diameter, resistance per meter, and max current for each gauge.