Hi, Apologies if this has been posted/answered else where but I could not find it. I am trying to develop a model in matlab for a simple (short cylindrical coil) air cored transformer. So far I am capable of defining the coil such as core diameter, turns, length etc.., calculate the coil resistance, input current, magnetic field produced, flux density at a given distance along the central axis, and potential emf for the secondary coil. The next thing I need to work out is the impedance Z. Z = sqrt(R^2 + X^2) where X = XL - XC I can calculate XL because I have found an equation to work out the inductance of the coil, L. L = (r^2 * N^2)/(9r + 10l) *from the wiki inductor page so XL = 2πfL. I run in to problems with capacitive reactance XC. I cannot find anywhere online explaining how to work out the capacitance of a coil so I can calculate the capacitive reactance XC. XC = 1/(2πFC) Does anyone here know how to calculate the capacitance of a coil, or even if my understanding is completely off?