Coil calculator APK

For example: resonant frequency from L and C, reactance from frequency and capacity etc.

The drop down menus on the right set the unit and with it the function. This shared functions allow the application to fit on the smallest of smartphones without scrolling.

There are basically 2 modes: inductance and LC, set by the 5th menu.
The length units and the Al are used in inductance calculations.
Reactance and admittance are related to L, C and f calculations.
When only the diameter and wire size is filled in, X calculates the impedance of an air filled coaxial line.

The right-hand menus also perform unit conversions, like Hz - rad/s, AWG - SWG - mm, resistance - conductance, fractional inches such as 1”¾ to SI (not the other way though).
The bottom right menu sets the inductance calculation algorithm:

Classical “Wheeler”. If the number of turns does not fit on a single layer, the multi-layer version is used.
“Zwicky” which takes into account all corrections to Wheeler
“Al” for toroïds and pot cores
No space “ooooo” and single wire thickness spaced “o o o o“ single-layer coils. As the input of most algorithms for inductance are the length and the number of turns (on which the length depends) this option gives a rough estimate of turns and length given only the inductance, diameter and wire size.
“Wire”: inductance of a straight wire
“GP”: inductance of a wire over a ground-plane.
The bottom row shows the total wire length and resistance, taking the skin effect into account. Only copper and silver “Ag” are available as material.

Toroid picture from http://hiqsdr.com/