This page is used to calculate different types of air coils. For best result always use the formulas without (...) after.

The basic formula to calculate inductance is: inductance=permability*turns*turns*area/length, the problem is that the result are not very exact when compared to a real coil. To give results that are closer to real world values some other formulas was made (Wheeler, Blakey) for specific coil geometries. They are simple and give better results than the basic formular. But even better formulas has been made, they are not simple, but the result are usual very close to the correct value (This program are using these formulas).

Geometries supported

Flat spiral, good result
Flat spiral (Simple), simple formula
Loop circular (Simple), can be used for a loop with one or more turns
Loop rectangular (Simple), can be used for a rectangular (or square) loop with one or more turns
Multi layer, advanced calculation of a multi layer coil
Multi layer (Blakey), a classic and simple formula for a multi layer coil
Multi layer square (Simple), a simpel formula for a multi layer square coil
Single layer, advanced calculation of a single layer coil
Single layer (Current sheet), assumes that the current is evenly distributed around the coil
Single layer (Wheeler), a classic and simple formula for a single layer coil
Single layer rectangle, a rectangluar coil with one layer
Single layer square, a square coil with one layer
Wire, inductance of a piece of wire
Wire pair, inductance of a two wires (Remark: "Side" is distance between wires)

All names with (...) after has lower precision or some restrictions.
When the graphic shows two yellow squares, one is a look from the end of the coil, but without the turns illustrated.

Input values

Turns	Number of turns on coil
Length	Length of coil
Diameter Ømin	Inner diameter of coil
Diameter Ømax	Outer diameter of coil
Wire diameter	Wire diameter, use Wires page to convert units
Bundle diameter	Diameter of wire bundle on a "circular loop" coil
Side	One of the sides on a square/rectangular coil
Side 2	The other side on rectangular coils
Winding thickness	Thickess of winding layer
Frequence	Frequence used on coil/wire, used to compensate for skin effect
Fill factor	Defines how tight the wire is wound (100 means no space for air or isolation)

Note: All measurement inputs, except wire diameter, are in meters.

Output values

Inductance	The estimated inductance, the error is depending on formula, how exact the coil is constructed, any iron in the vicinity and frequence
Coil length	Lenght of coil, this is the same value as the input value "Length"
Avg. coil diameter	Average diameter, this is diameter_Ømin+winding_thickess
Avg. side	Average side, this is side+thickess of copper
Avg. side 2	As above, but for long side on rectangles
Winding thickness	The thickness of the windings
Wire length	Total length of wire use for this coil
Resistance	Resistance in wire
Estimated weight	Weight of wire

Hints

Fill factor is only used in design
In design use "Fill factor" (on config page) to change the length of the coil
Keep an eye on the copper mass. If it show a couple of Kg, it is a BIG coil
Most formulas do not warn when using invalid geometries
Wire pair: "Side" is distance between wires, "AvgSide" is distance between wire centers
"To analyze" button only copy visible digits. If "Fill factor" is high, analyze may think there is to much copper and mark one of the dimensions in red
"To analyze" button only copy visible digits. This may change the inductance a little
It is possible to leave "Wire diameter" empty in "Analyze" for some geometries, it will not change the result
Small changes to the dimensions of a coil may give big changes to the inductance
To enter a value in inch, use the calculating ability of the input field. i.e. 3 inch is entered as "3*inch". This constant comes from the Calculator const page (This does NOT work for the wire diameter field, it expects input in mm, not meter)

Other pages

For calculation charge/discharge curves use Charge curve page.
For calculation impendance of a inductor use Ohms law page.

MiscEl: Air coil

Geometries supported

Input values

Output values

Hints

Other pages