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 sseveral authors/webprogrammers have taken the underlying formulas for inductor design and created online calculators which help determine the physical parameters required for a coil with the desired electrical properties. Listed below are links to online 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 browserbased 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 noncoil 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 inches  Does singlelayer and multirow multilayer
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 singlelayer
and multirow multilayer 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
selfcapacitance
Several Step Coil Design
Input size in mm  Computations for
several coil properties  With examples
LF
Inductance Calculator
 Dimensions in mMeters 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
Inductance of singlelayer coils on
cylindrical forms  Input the radius, length, permeability
and # of turns  computes uH
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
SingleLayer
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
Professor Coyle's Cylindrical Coil Calculator
 Does both close wound and space wound coils  Read the instructions
first
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
selfcapacitance
Coil Design and Inductance Calculator
 Input: dimensions in metric units or inches  Calculates inductance
in uHenrys
Inductance
of SingleLayer Coils  Input:
Turns, dimensions in mMeters and Perm.  Calculates L on a new page
Calculates Inductance of Circular Loop

Input: Turns, dimensions in mMeters 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.
Amidon Toroid Calculator (Ferrite)
 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
Some
help working with toroids: (Also see the last
section Additional
Coil
Information below)
Toroid
Specification Chart  For 88 toroids  with flexible
calculator
Toroid
Characteristic Charts  Eight charts of data on toroids
GQRP
Club Toroid Information  For common toroids  includes AL
data
GQRP Club Toroid Inductance Chart
 A PDF of mHenrys values for
many colorcoded
toroids
with 1 50 turns
What material is this?  My PDF
collection of toroid material identification methods
Toroids  Some Practical Considerations
 Detailed article  with power ratings (Watts) for many
common toroids
The SelfCapacitance of Toroid
Inductors  Perhaps more than you need to know about
selfcapacitance in coil design
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 uMeters  Does several flat shapes  Other
calculator links here
SingleLayer
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
Professor Coyle's Spiderweb Coil Calculator
 Nice  Includes wire table and resonance calculator  Read the
instructions below
Solenoid  Multilayer Coils:
Multilayer
Air Core Inductor Calculator
 Choice of units  Inputs: L, Coil
diameter and length, wire gauge  Multiple outputs
Multilayer Air Core Inductance Calculator
 Choice of units  Complex inputs because of layers  Only useful
below 3 MHz
MultiLayer 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
Other Calculators:
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.
WA4DSY's RF Filter Design Site
 Does several filter types with output plots  Really
helpful; a keeper
Turns Ratio Calculator 
Does the turns ratio squared thing.
RF Cafe's Skin Depth Calculator 
Infrequently needed, but from a great site for RF Engineers and Hams
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
Additional Coil Information:
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.
PDF  Measuring Soft Ferrite Core Properties
 A fourpage PDF of measurement information.
All About Ferrite from Nuts
& Volts Magazine  A good education with references
at the end
### 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.
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Site  The Marine Radio History Archive
Created on 11/11/2018  Page code updated 02/26/2021