Help! - Coil Resistance Calculator

I started out making this calculator before I had a meter to accurately check the resistance of the coils I made. I do have an ohm (resistance) meter now to check the coils, but I still find this calculator very handy to use and accurate at projecting the outcome of a coil. Typically my calculated values will show something like 2.15 Ω while the meter will show something like 2.19 Ω, so I do consider the calculator to be very accurate, but that depends on accuracy of the input values.

Kanthal AWG: I've only made coils using 30 gage Kanthal A1, so feedback as to the accuracy with Kanthal D and Nichrome 60 is very welcome. Please email me jp@purelogicco.com with your results provided you do have an ohm meter for low resistance and you know the specific wire used.       I've noticed sites giving a simple resistance value per inch, first of all no manufacturer gives the resistance per inch for anything more than a value to estimate with. The resistance value can be determined with the below formula using the resistivity of metal round wire.

formula is: R = Resistance in Ω (Ohms) ρ (rho) = resistivity l = length of wire (in meters) A = Area of the wire's cross section

Resistivity values I used are:       Kanthal A-1 is 1.45 Ω mm2 / meter       Kanthal D is 1.35 Ω mm2 / meter       Nichrome 60 is 1.11 Ω mm2 / meter

Coil ID: This is typically the diameter of the drill bit, pin, shaft, etc. that your coil is turned on, thus becoming the coil's ID (inside diameter). The ID is used (with the wire thickness) to determine the coil's circumference and eventually the length of wire needed for each turn. If you are turning your coil directly on silica, cotton etc. then you will need to estimate the ID value.       Because kanthal stretches and springs out to a slightly larger size than the shaft used, I add about 0.01" (eg. for 1/8" (0.125) I input 0.135") to the shaft's diameter. Your milage may vary, so experiment with it and find what works for you.

Coil Turns: This is the amount of turns (or wraps) used to make your completed coil. You may have seen for example: "7/8" for the amount of turns, 7 on the coil's bottom (or underside) 8 on top, or "4/5", for 4 on bottom, 5 on top. I think it's foolish and I refuse to consider them in that way. I much prefer to consider the exact amount of coils, so for a 7/8 in the example I consider this to be a 7.5 turn coil and input it as such. If your coild has 8.5 coils then input 8.5, if it has 8 coils then input 8.

Lead Length: If you use resistance wire for the leads to your coil - input it's length here, as it has resistance also and should not be ignored. If you use a non-resistance wire as a lead to the coil please input zero (0) for your length. Since there is only one input add your leads and enter the total amount (eg. two 1/8" (0.125) leads will be 1/4" so enter ".25". This value should be measured along the straight lead from mid coil to the closest point of contact to your base and center pin.       You can also find the resistance of a piece of wire by entering the length, selecting a wire type and gage and click calculate.

Total Wire: this output shows the amount of wire required to create a coil with the parameters you've entered into the calculator. This is a total wire length for the coil and any lead length you've specified.

Total Ohms: this is what the calculator is all about, finding the Ω for a given wire size and coil diameter. The output is approximately what you should see on a meter when testing a coil made with the parameters given.