# Coil Inductance Calculator

## Use the Coil Inductance Calculator to calculate the inductance of air-cored single-layer solenoid, multi-layer solenoid and flat spiral coils

The formula for calculating the inductance of an air-core single-layer solenoid is:

$L= \frac{r^2N^2}{9r+10l}\; \mu H$

The formula for calculating the inductance of an air-core multi-layer solenoid is:

$L= \frac{0.8(r^2N^2)}{6r+9l+10d}\; \mu H$

The formula for calculating the inductance of an air-core flat spiral coil is:

$L= \frac{r^2N^2}{8r+11d}\; \mu H$

Where
N = Number of turns
r = Coil radius in inches
l = Coil length in inches
d = Winding depth in inches
L = Inductance in microhenrys (μH)

Coil dimensions for calculating inductance

### Using the Coil Inductance Calculator

Coil Geometry: Select the geometry of your coil from the list. You can choose from single-layer solenoid, multi-layer solenoid and flat spiral coil forms.

Length: Enter the coil length, measured as depicted in the diagram above.

Diameter: Enter the coil diameter, measured as depicted in the diagram above.

Depth: Enter the winding depth, as depicted in the diagram. This does not apply to a single-layer solenoid coil.

Number Of Turns: Enter the total number of turns.

Select Units: Select the units that you used for your coil dimensions from the list, and select your preferred output units of inductance.

Reference: ARRL – The Radio Amateur’s Handbook

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