TYPE
SHAPE
Please enter all required numeric values.
RESULTS
Calculated Inner Diameter
µm
Input Parameters Specification
Coil TypeSelect Single Layer, Multi Layer, or Flat Planar Spiral Coil.
DiameterDiameter selector supports mm, cm, and inch for single and multi coil modes.
Length / DepthSingle coil uses coil length; multi coil uses length plus winding thickness/depth.
TurnsNumber of turns directly affects inductance because N is squared in the formula.
Relative Permeability μrUse 1 for air core. Ferrite or magnetic core materials may need higher μr.
Flat Spiral ShapeSquare, hexagonal, octagonal and circular shapes use different planar constants.
Practical Operational Examples
Single Layer RF Coil
Use diameter, coil length, turns and μr = 1 for an air-core RF coil used in LC tanks or antenna matching.
Multi Layer Coil
Use average diameter, length, winding depth, turns and permeability for thicker wound inductors.
PCB Spiral Inductor
Use flat mode for square, hexagonal, octagonal or circular planar spiral layouts.
Ferrite Core Estimate
Change μr when estimating a magnetic-core coil, but verify with measurement for final hardware.
Diagrams & Theory
These custom SVG diagrams show single coil, multi-layer coil, and four flat spiral inductor shapes arranged in one line.
Formulas & Mathematical Logic
Single layer: L(µH) = (r² × N² × μr) / (9r + 10l)
Multi layer: L(µH) = (0.8 × r² × N² × μr) / (6r + 9l + 10d)
Flat mode: delta = n × (w + s) - s; Din = Dout - 2 × delta; Davg = Dout - delta; p = (Dout - Davg) / Davg.
Flat mode uses Modified Wheeler, Current Sheet and Monomial Fit constants for the selected shape only.
Step-by-Step Example
Single layer example: diameter = 25 mm, length = 50 mm, turns = 20, μr = 1.
Convert dimensions to inches, then r = diameter / 2.
Apply Wheeler formula and display µH, mH and H.
Flat example: n = 5, w = 10 µm, s = 2 µm, Dout = 250 µm. delta = 58 µm, Din = 134 µm.
How to Use This Calculator
Select Single, Multi, or Flat Planar Spiral Coil.
Enter coil geometry and select units where available.
For Single or Multi, enter relative permeability μr.
For Flat mode, choose Square, Hexagonal, Octagonal or Circular shape.
Press Calculate to display results.
About This Calculator
Calculate inductance for wound coils and PCB-style planar spiral inductors.
This CalcBoy calculator combines three practical coil design modes in one lightweight tool.
The Coil Inductance Calculator helps estimate inductance for single layer solenoid coils, multi-layer windings, and flat planar spiral inductors. Single and multi-layer modes are useful for RF coils, air-core inductors, ferrite-core windings, sensor coils and custom electromagnet design. Flat mode is useful for PCB spiral inductors and IC-style planar inductor layouts.
Single LayerBest for simple air-core coils, RF tank circuits and antenna matching coils.
Multi LayerUseful for thicker windings where coil depth affects inductance.
Flat SpiralSupports square, hexagonal, octagonal and circular planar spiral shapes.
Design NoteReal inductance changes with frequency, parasitic capacitance, wire diameter and core losses.
Tip: For RF or high-current designs, always verify calculated inductance with an LCR meter or VNA before final hardware use.
Frequently Asked Questions
What is coil inductance?
Coil inductance is the ability of a winding to store magnetic energy when current flows through it.
What does μr mean?
μr is relative permeability. Use μr = 1 for air-core coils and higher values for magnetic materials.
Why are there three flat spiral formulas?
Modified Wheeler, Current Sheet and Monomial Fit are different published approximation methods for planar spiral inductors.
What is calculated inner diameter?
It is the inner opening left after subtracting turns, trace width and spacing from outer diameter.
What is fill factor p?
It describes how tightly the spiral is packed according to the average diameter relation used in the formula.
Are these results exact?
No. They are engineering estimates. Real measured inductance may vary due to construction and material effects.
Can I use this for PCB inductors?
Yes, use Flat Planar Spiral Coil mode and select the matching shape.
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