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Introduction

This page contains two inductor calculators. With both calculators, the main limitation is that they be Single-Layer Air-Core inductors. The first one, below, uses formula published in the ARRL Handbook For Radio Amateurs, and many others. It's nice because it requires only a few inputs to get a estimate of the inductor.

Both calculators come up with inductance estimates that are very close. The second method, however, provides more information, like Reactance, Q, and Self Resonant Frequency.

Coil Inductance Estimating Calculator Ⅰ
Input Data
Coil Diameter
Coil Length
Number of Turns
Output Data
Inductance (uH)
Coil Turns Spacing

This is a very simple calculator for estimating the inductance of a Single-Layer Air-Core inductor. The program uses formula published in the ARRL Handbook For Radio Amateurs and other radio publications.

In the text areas provided, enter the Coil Diameter, Coil Length, and Number Of Turns. You can use either inches or millimeters and you can mix and match. The estimated Inductance, in uh, and Coil Turns Spacing will be calculated. Recalculation is automatic. Just click outside the entry area after changing any input data.

The formula is correct to 1%, provided that L > 0.8 × D/2, i.e. the coil is not too short.

If you need a more accurate reading, or the coil does not meet the Single-Layer Air-Core coil criteria, use an Inductance Bridge or Grid-Dip Meter to determine the inductance.

Coil Inductance Estimating Calculator Ⅱ

This calculator, takes into account the wire size and wire composition. It was addressed by Serge Stroobandt, ON4AA on http://hamwaves.com/antennas/inductance.html. Please refer to that site for detailed information. I only reconfigured it a bit to make it easier to use.

Input Data
Mean Diameter (D)
of the air core coil.

Number of Turns (N)
Length of the coil (L).
Wire Diameter (d)
Plating Material
Plating Conductivity ρ = x nΩm
Plating Permeability μr =
Design Frequency MHz

The table below lists some of the results from intermediate calculations and the final output. Of particular interest might be the Effective Wire Length. That value would be useful when you are creating a shortened dipole or a multiband dipole. For a shortened dipole, the Effective Wire Length indicates the reduction in length, for the wire past the inductor.

Intermediate Results
Winding pitch. p = mm
Proximity factor. Φ =
Effective coil diameter. Deff = mm
Correction factors
Field non-uniformity
correction factor.
kL =
Self-Inductance, Round
wire correction factor
ks =
Mutual-Inductance, Round
wire correction factor
km =
Wire
Physical wire length. wire =
Effective wire length. wire, eff =
Skin depth at
design frequency.
δi = µm
Sheath helix waveguide mode
Effective pitch angle. ψ = °
Axial propagation factor. β = rad/m
Characteristic impedance. Zc = Ω
Final Output Data
Results (at design frequency)
Effective series inductance. LEff,s = µH
Effective series reactance
of round wire coil.
XEff,s = Ω
Effective series AC resistance
of round wire coil.
REff,s = Ω
Effective unloaded quality
factor of round wire coil.
QEff,ul =
Lumped circuit equivalent
Frequency-independent
series inductance.
Ls = µH
Series reactance of
round wire coil.
XL,s = Ω
Series AC resistance
of round wire coil.
RL,s = Ω
Unloaded quality factor
of round wire coil.
QL,ul =
Parallel stray capacitance. CL,p = pF
Self-resonant frequency
Self-Resonant Frequency,
λ/4 (parallel)
fres,L = MHz