Calculator Inputs
Plotly Graph
This curve shows how inductance changes as turns increase for the selected geometry.
Example Data Table
| Model | Example Inputs | Approximate Inductance | Use Case |
|---|---|---|---|
| Air-Core Solenoid | 120 turns, 25 mm diameter, 40 mm length, μr = 1 | 222.0661 µH | General prototype coil estimate |
| Toroidal Core | 80 turns, 20 mm ID, 36 mm OD, 8 mm height, μr = 60 | 0.351086 mH | Compact magnetic core design |
| Square PCB Spiral | 12 turns, 10 mm inner, 30 mm outer, effective μr = 1 | 3.56578 µH | Early planar inductor layout |
Formula Used
Air-Core Solenoid
L = μ0μrN2A / l
Use this for cylindrical coils. Here, A is the circular cross-sectional area and l is the magnetic length of the winding.
Toroidal Core
L = μ0μrN2A / lm
This uses core area A and mean magnetic path length lm. It gives quick toroid estimates from basic dimensions.
Square PCB Spiral
L ≈ 2.34μ0μrN2davg / (1 + 2.75φ)
This approximation is useful during layout planning. davg is average diameter and φ is fill ratio.
How to Use This Calculator
- Select the inductor model that matches your geometry.
- Enter turns and the required physical dimensions in millimeters.
- Set relative permeability for air, ferrite, or other materials.
- Add operating frequency to estimate inductive reactance.
- Add current to estimate magnetic energy storage.
- Choose the output unit you want to review.
- Press the calculate button to show the result above the form.
- Use the export buttons to save your result as CSV or PDF.
FAQs
1. What does inductance measure?
Inductance measures how strongly a conductor resists current change by storing magnetic energy. Higher inductance usually means greater opposition to changing current at a given frequency.
2. Why does inductance rise with turns?
Inductance grows roughly with the square of turns in these models. Doubling turns can increase inductance about four times when the rest of the geometry stays unchanged.
3. When should I use the solenoid model?
Use the solenoid option for cylindrical windings on air or simple formers. It works well for early design estimates, lab coils, and educational engineering calculations.
4. When is the toroidal model better?
Choose the toroidal model when the winding wraps around a ring-shaped magnetic core. It is useful for compact inductors, filters, power stages, and low-leakage magnetic designs.
5. Is the PCB spiral result exact?
No. The spiral method is an approximation for concept design. Trace width, spacing, copper thickness, shielding, and nearby conductors can shift the actual measured inductance.
6. What is inductive reactance?
Inductive reactance is the AC opposition produced by an inductor. It increases with both frequency and inductance, following XL = 2πfL.
7. Why does material permeability matter?
Relative permeability describes how easily magnetic flux forms inside a material. Higher permeability generally raises inductance, especially in toroidal and core-based designs.
8. Should I still validate the design physically?
Yes. Real inductors depend on winding resistance, gaps, fringing, saturation, parasitics, and tolerances. Use this calculator for design direction, then confirm with measurement or simulation.