Helical Coil Calculator
Calculate inductance of helical (solenoid) coils using Wheeler's formula
Millimeters (mm)
Millimeters (mm)
Number of wire turns
How to Use This Calculator
Enter Coil Diameter
Enter the coil diameter in millimeters (mm). This is the outer diameter of the coil.
Enter Coil Length
Enter the length of the coil in millimeters (mm). This is the length along the coil axis.
Enter Number of Turns
Enter the number of wire turns in the coil.
Get Inductance
Click calculate to see the coil inductance in microhenries (µH), millihenries (mH), or nanohenries (nH).
Formula
L = (d² × n²) / (18d + 40l)
(Wheeler's formula for helical coils)
Where:
- L = Inductance (µH)
- d = Coil diameter (inches in original formula, converted here)
- n = Number of turns
- l = Coil length (inches in original formula, converted here)
Note: This calculator uses Wheeler's formula, which is accurate for air-core coils. For ferrite-core coils, inductance will be higher due to core permeability.
Example:
Diameter = 10 mm, Length = 20 mm, Turns = 100
L = (10² × 100²) / (18 × 10 + 40 × 20) = 1,000,000 / 980 = 1,020 µH
About Helical Coil Calculator
The Helical Coil Calculator calculates the inductance of helical (solenoid) coils using Wheeler's formula. Helical coils are common in RF circuits, filters, and inductor applications. This calculator helps design coils for specific inductance values.
When to Use This Calculator
- RF Circuit Design: Design coils for RF filters and matching networks
- Inductor Design: Calculate inductance for custom inductor designs
- Educational Purposes: Learn about coil inductance calculations
- Circuit Analysis: Analyze existing coil circuits
Why Use Our Calculator?
- ✅ Accurate Calculations: Uses Wheeler's proven formula
- ✅ Easy to Use: Simple interface
- ✅ Free Tool: No registration required
- ✅ Educational: Includes formulas and examples
Common Applications
RF Filters: Helical coils are used in RF bandpass and bandstop filters. The inductance determines the filter's resonant frequency and bandwidth.
Matching Networks: Inductors in impedance matching networks use helical coils for their predictable inductance values.
Tips for Accurate Results
- Enter dimensions in millimeters
- Wheeler's formula is accurate for air-core coils
- For ferrite cores, multiply result by core permeability
- More turns increase inductance
- Larger diameter increases inductance
Frequently Asked Questions
What is Wheeler's formula?
Wheeler's formula is an empirical formula for calculating the inductance of helical coils. It's accurate for air-core coils and accounts for the coil's geometry (diameter, length, and number of turns).
Does this work for ferrite-core coils?
Wheeler's formula is for air-core coils. For ferrite-core coils, multiply the result by the core's relative permeability (typically 100-10,000 depending on material).
How does coil geometry affect inductance?
Inductance increases with the square of the number of turns and the square of the diameter. It decreases with increasing length. More compact coils (shorter length, larger diameter) have higher inductance.