Radio home brewers have an easy time working with resistors and capacitors; they come in neat little packages and their values are easily determined, but working with inductors isn't as easy. To obtain the inductance and other characteristics desired, coils often can't be purchased and must be custom wound. Coil design/creation include selecting the proper coil shape, wire size and core material (if not air), all making the process a little complex, Fortunately several authors/web-programmers have taken the underlying formulas for inductor design and created on-line calculators which help determine the physical parameters required for a coil with the desired electrical properties. Listed below are links to on-line calculators helpful in designing coils for radio applications. Look around on these sites as some of them list other useful calculators.

To the best of my knowledge at the time of the creation of this page all of the links are to free calculators with no registration required for use. As I have only used some of these I make no recommendations, and the listing order does not indicate any preference. The information about each may help you choose those best meeting your needs. It's worth noting that the authors of some are critical of the accuracy of the formulas used by others. Many thanks to the authors for their work in making these browser-based design aids available.

### Indicates the calculators that go beyond simply solving the equation for one stated missing value by finding any missing value provided the other values are entered.

Multiple Calculations or Coil Configurations:

Three Inductance Calculators - Units: nHenrys, uHenrys & mHenrys - Computes Number of turns, AL and L

Coil Inductance and More - Several choices of units - Output is Inductance - Calculators for several non-coil shapes are available

Coil Inductance Calculator - Several
choices of units - Computes Inductance for single/multi layer solenoids
and flat spiral coils

Find L for Coils and Other Shapes
- Several choices of units +
Permeability - Output is Inductance

Two coil Inductance Calculators -
Inputs in inches - Does single-layer and multi-row multi-layer coils.
Computes L

Five Coil/Inductance Calculators - Several inductor calculators using different knowns for inputs - Dimensions in mm

Three Coil/Inductance Calculators - Inputs in cm or inches - Does single-layer and multi-row multi-layer coils. Computes L

Three More Coil/Inductance Calculators - Some choice of units for inputs - 2 outputs are Inductance - The other is Reactance

Single Layer Air Core Coils:

Air Core Inductor Calculator - Wide choice of coil size units - Computes Inductance with choice of units

Air Core Inductor Designer - Calculator - Input in mHenrys and inches - Extensive output on a new page

Air Cored Inductor Calculator - Includes Q - Size units in mm - Computes Inductance, Q and wire length

AL Inductance Calculator ### - Input two values and get the third - Inductance units: mHenrys, uHenrys, nHenrys

Coil Inductor Calculator - Size units in inches - Computes Inductance in uHenrys and wire length in inches and feet

Two Coil Calculators
- Inputs size in mm or inches and Turns - Computes Inductance and
number of turns

Helical Coil Calculator - Input size in mm or inches - Computes Inductance and wire length - Includes self-capacitance

Several Step Coil Design - Input size in mm - Computations for several coil properties - With examples

LF Inductance Calculator - Dimensions in Meters and MHz (for Q) - Result in microHenrys and Q

Single Layer, Air Core, Inductance Calculator - Dimensions in mm & MHz (for Q) - Computes L in multiple units & wire length

Air Core Inductance Calculator -
Dimensions in inches - Output in
uHenrys

LC Inductance Calculators
- Input Turns, coil and wire diameters in inches -
Computes uHenrys and wire and coil
lengths

Air Core Coil Inductance Calculator - Input Turns, coil diameter and length in inches- Calculates L in uHenrys

Single-Layer
Air Coil Calculator
- Wide choice of units - Input L, coil and wire diameters - Computes
Turns and coil length

Single Layer Air Coil Calculator ### - Entry boxes are Turns, diameter, length and L - Enter 3 get the 4th. - With examples

Another Single Layer Air Coil Calculator - Choice of units - Input L, coil and wire diameters - Computes Turns and coil length

Two Coil Calculators - Choice of units - One calculates L, the other Turns and winding length

Single Layer Coils Over A Magnetic Material:

Universal Single Layer Calculator ### – Input: 4 parameters & get the 5th - Can be used to find unknown core Permeability

Comprehensive Coil Calculator - Too extensive to summarize - Take a look at it - Includes self-capacitance

Coil Design and Inductance Calculator - Input: dimensions in metric units or inches - Calculates inductance in uHenrys

Inductance of Single-Layer Coils - Input: Turns, dimensions in Meters and Perm. - Calculates L on a new page

Calculates Inductance of Circular Loop - Input: Turns, dimensions in Meters and Perm. - Calculates L in Henrys

Finds Inductance of Single Turn Solenoid - Choice of units - Input: Turns, length radius & Perm. - Output L in multiple units

Cylindrical Coil Inductor Design Calculator ### via 4 calculators - Choice of units - Calculates L, turns, perm., area, & length

Toroid Coils:

Amidon Toroid Calculator (Iron Powder) - Input desired uHenrys and Amidon core size and color to find L, turns, etc.

Ferrite Core Inductor Calculator - Input number of turns and AL to find coil Inductance

Inductance of a Toroid - Input core dimensions in cm, number of turns and permeability to find coil Inductance

Toroid Inductance Calculator - Input core dimensions in mm or mils, number of turns and permeability to find coil Inductance

Toroid Inductance Per Turn Calculator - Wide choice of input units & number of turns - Outputs L and other characteristics

Two Toroid Inductor Calculators - Wide choice of input/output units & number of turns - Outputs L and other characteristics

Toroid Winding Calculator - Finds number of turns for powered iron and ferrite cores of known size and material composition

Spiral (Flat) Coils:

Flat Spiral Air Core Coil Inductors - Many choices of units for dimensions - Finds Inductance - Five other coil calculators here

Flat Spiral Coil Calculator - Accepts dimension inputs in inches or mm - Output in uHenrys

Planar Spiral Coil
Inductor Calculator
- Dimensions in mMeters - Does several flat shapes - Other
calculator links here

Single-Layer Flat Air Coil Calculator - Accepts dimension inputs in inches or mm - Output in uHenrys or nHenrys

Spiral Inductor Calculator - Dimensions in mMeters - Nine outputs, for different shapes and formulas, are calculated

Spiral Coil Calculator - Dimensions
in mm & number of turns - Output
in uHenrys - Uses Wheeler's formula

Solenoid - Multi-layer Coils:

Multilayer Air Core Inductor Calculator - Choice of units - Inputs: L, Coil diameter and length, wire gauge - Multiple outputs

Multi-layer Air Core Inductance Calculator - Choice of units - Complex inputs because of layers - Only useful below 3 MHz

Multi-Layer Coil Inductance Calculator - Air Core - mm or inches - Complex inputs because of layers - Multiple outputs

Coil Physical Properties Calculator
– For relay solenoid coils - Not for RF

Permeability
- Find the
Permeability of an unknown core:

Determine Toroid Permeability - Inputs in mHenrys to nHenrys and mm or cm core dimensions - Output is Perm. & AL

How to Determine Permeability of Unknown
Cores - Inputs in uHenrys
& dimensions in mm - Also Inductance calculator

See
also: Universal Single Layer Calculator ###

Reactance:

Inductive Reactance Calculator - Accepts inputs in Hertz to GHz and nHenrys to Henrys

Inductor Impedance Calculator - Accepts inputs in Hertz to MHz and pHenrys to Henrys

Reactance Calculator R L C ### - Units are fixed: uFarads, mHenrys & Hertz - Links to capacitive Reactance calculator

Reactance Calculator for Both L & C - Units are fixed: pFarads, uHenrys and MHz

Mutual Inductance Calculator - Calculates Mutual Inductance given 2 coils Inductance (in mHenrys) & their coupling factor.

Another Mutual Inductance Calculator - Like above but offers a choice of units.

Turns Ratio Calculator - Does the turns ratio squared thing.

Wire Self Inductance Calculator - Choice of input units - Calculates L, in nHenrys, of a length of wire

Comprehensive Tesla Coil Design - Not useful for RF?

More Tesla Coil Calculators - Not useful for RF?

Balun and Transformer Core Selection - Much useful information and links from W8JI

Wire, Toroids, and Transformers - Much useful information - Includes wire gauge table and more.

The Self-Capacitance of Toroid Inductors - Perhaps more than you need to know about self-capacitance in coil design.

PDF Toroid Inductance Chart - A PDF table of the mHenrys values for common color-coded toroids with 1 to 50 turns.

PDF - Toroid Identification - A two-page PDF of notes on ferrite core identification

PDF - Measuring Soft Ferrite Core Properties
- A four-page PDF of measurement information.

### Indicates the calculators that go beyond simply solving the equation for one stated missing value by finding any missing value provided the other values are entered.

Please contact me about other applications of this type and about any corrections to the information on this page.