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/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:
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 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
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 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 single-layer 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
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
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
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 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
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)
Specification Chart - For 88 toroids - with flexible
Toroid Characteristic Charts - Eight charts of data on toroids
G-QRP Club Toroid Information - For common toroids - includes AL data
G-QRP Club Toroid Inductance Chart - A PDF of mHenrys values for many color-coded 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 Self-Capacitance of Toroid Inductors - Perhaps more than you need to know about self-capacitance 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
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
Professor Coyle's Spiderweb Coil Calculator - Nice - Includes wire table and resonance calculator - Read the instructions below
Solenoid - Multi-layer Coils:
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
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 ###
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.
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:
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 four-page 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.
Created on 11/11/2018 - Page code updated 02/26/2021