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
Results
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.