I have incorporated two Coil Calculators, one tells the Resonate Frequency of a coil with a capacitor connected in parallel. The other lets you figure the turns of wire to achieve the desired inductance you need.
Below is the LC Calculator. For typical Crystal Radio Coils select Pico-Farads ( this is same as PF ). For the Inductance select Micro-Henries ( this is same as uh ). For the Resonate Frequency select Kilo-Hertz or Mega-Hertz. (500 KHz = .500 MHz and 1800 KHz = 1.800 MHz etc.)
Leave Resonant Frequency Blank.
For instance to check if a crystal radio coil design calling for a 20pf to 384pf variable capacitor will work to cover the AM radio band with a 240uh coil. For Capacitance select Pico-Farads then put 20 in the box, next for inductance select Micro-Henries and put 240 in the box. Next for frequency select Kilo-Hertz or Mega-Hertz then press Calculate. Do the same for 384pf only change the 20 to 384 and press Calculate.
Below is the Calculator to figure the Inductance of a coil by entering the Coil Diameter and Wire Diameter and Number of turns. Leave Blank Inductance, Wire Length and Coil Length. The length of wire needed to make the coil does not include the lead length you may need so if you need 6 inches from each end of the coil add a foot to the length. The coil length is the length of the coil on the form you are winding it on. This will help to design a coil by figuring its inductance.
Below are the approximate wire diameters for various enamel coated copper wire sizes.
Please note that this is for heavy build wire and wire with more or less enamel coating may vary several thousandths of and inch plus or minus.
22 Awg Gauge About .0276 in diameter.
24 Awg Gauge About .0223 in diameter.
26 Awg Gauge About .0178 in diameter.
28 Awg Gauge About .0144 in diameter.
30 Awg Gauge About .0116 in diameter.
32 Awg Gauge About .0094 in diameter.
34 Awg Gauge About .0075 in diameter.
36 Awg Gauge About .006 in diameter.
38 Awg Gauge About .005 in diameter.
39 Awg Gauge About .0043 in diameter.