# Calculation of inductance coil

Calculation of inductance coil

Inductance coil may be represented by a screw, spiral, or screw-spiral coil made of a folded insulated conductor. The coil has significant inductance at a relatively low capacitance and low active resistance.

Coil's inductance depends on its geometrical dimensions, number of windings, and winding methods. Bigger diameters, winding length and a greater number of windings result in greater inductance. Sometimes you need to wind the coil according to the specified dimensions but you don't have a wire with necessary diameter. In this case you have to somewhat increase the number of winding coils when winding it with a thicker wire, and vice versa - you have to decrease it when winding it with a thinner wire. In this way you'll get the necessary inductance.

All such considerations are fair when winding coils without ferrite cores which are very often found in various radio-receiving and transmitting sets, especially in those which are made in China. You won't find labeling on the wire spring as it's not specified. However, you may need to know inductance of such coil. To do this, you can use the formula for calculating one-layer cylindrical coils, where L is the coil's inductance in microhenries. D is the coil's diameter in cm. L is the winding length in cm. N is the number of windings.

You can derive any value from this formula - for example, the number of windings at a known diameter and specified inductance, or the coil's diameter at a limited winding length.

It is recommended to use the specified formula for calculating such coils in which winding length l equals or exceeds half of diameter.