How geometry affects inductance
More turns, a larger average diameter and a larger fill factor all increase inductance. The same copper area can give different results depending on width, spacing and shape.
Planar inductor
Estimate the inductance of a planar PCB spiral from its geometry and shape.
Result
Enter your values to calculate a result.
The illustration shows a square spiral. Enter the outer diameter, trace width, gap and number of turns for your chosen shape. The estimate assumes a single layer.
Illustration only. Not to scale.Inductance
N/A
Inner diameterN/A
Fill factorN/A
Average diameterN/A
TurnsN/A
Method and assumptions
Inner diameter: din = dout − 2n(w + s) + 2s. Fill factor:ρ = (dout − din)/(dout + din).
Square, hexagonal and octagonal spirals use the modified Wheeler expressionL = K1 × µ0 × n² × davg / (1 + K2 × ρ). Circular spirals use the current-sheet expression.
- This estimates low-frequency inductance in free space. Ground planes and eddy currents in the substrate are not modelled.
- Self-resonance is not included.
- Best accuracy for fill factor above 0.1 and spacing at least 3× the conductor width.