# Air core coil inductance

Outer diameter
mm
Inner diameter
mm
Number of turns

An air core coil is a type of inductor that does not have a core made of a magnetic material, such as iron or ferrite. Instead, the core of the coil is simply the air that surrounds it. Air core coils are often used in applications where a high inductance is needed and where the coil will not be subjected to high temperatures or high levels of DC current.

To calculate the inductance of an air core coil, you will need to know the following information:

• The number of turns in the coil (N)
• The diameter of the coil (D)
• The length of the coil (L)

Once you have this information, you can use the following formula to calculate the inductance of the air core coil:

Inductance (in microhenries) = (0.00000125 x N^2 x D) / L

For example, if you have an air core coil with 300 turns, a diameter of 0.5 inches, and a length of 2 inches, the inductance would be:

Inductance = (0.00000125 x 300^2 x 0.5) / 2

Inductance = 0.5625 microhenries

It’s important to note that the above formula is an approximation and the actual inductance of an air core coil can be affected by many factors, such as the shape of the coil, the proximity of other magnetic materials, and the permeability of the surrounding air.

It is also important to note that the above formula is only valid for air core coils that are long and thin in comparison to their diameter. If the coil is short and wide, the actual inductance will be different.

To get a more accurate measurement of the inductance for your coil, you can use a specialized tool such as an inductance meter or an LCR meter.

In summary, calculating the inductance of an air core coil is relatively simple as long as you know the number of turns, the diameter, and the length of the coil. The formula provided is an approximation and actual inductance may vary due to many factors. It is also important to note that the formula is only valid for air core coils that are long and thin in comparison to their diameter.