Inductor / Coil Calculator
Calculate air-core coil inductance, LC resonant frequency, and inductive reactance. Built for RF designers and electronics engineers.
How the Inductor Calculator Works
Three modes for common inductor calculations in RF and power electronics.
Air-Core Coil
Wheeler's formula: L = (N² × r²) / (9r + 10l) in µH. Enter turns, diameter in inches, and coil length.
LC Resonance
f = 1 / (2π√(LC)). Enter any two of L, C, and f — the calculator solves for the third automatically.
Inductive Reactance
XL = 2πfL in ohms. Enter inductance and frequency to see the coil's AC impedance.
Common Ferrite Permeability Values
Typical relative permeability (μr) for common ferrite materials.
| Material | Permeability (μr) | Frequency Range | Application |
|---|---|---|---|
| Ferrite 43 | 850 | 1–30 MHz | EMI suppression, broadband |
| Ferrite 31 | 1500 | 0.1–10 MHz | Power line chokes |
| Ferrite 61 | 125 | 10–100 MHz | RF transformers, antenna |
| Ferrite 77 | 2000 | <1 MHz | Power converters |
| Iron Powder −2 | 10 | >30 MHz | RF inductors |
| Iron Powder −6 | 8 | >50 MHz | VHF inductors |
Frequently Asked Questions
Common questions about inductor calculations.
Use Wheeler's formula: L (µH) = (N² × r²) / (9r + 10l), where N is number of turns, r is coil radius in inches, and l is coil length in inches. This approximation is accurate for coils where l > 0.8r.
The resonant frequency of an LC tank circuit is f = 1 / (2π × √(L × C)). Given any two values, our calculator solves for the third. This is essential for tuning RF circuits, filters, and oscillators.
Inductive reactance XL = 2πfL is the opposition an inductor provides to AC current, measured in ohms. It increases with both frequency and inductance. At DC (f=0), an ideal inductor behaves as a short circuit (XL = 0).