Calculator
Example Data Table
| Example | Diameter mm | Length mm | Turns | Method | Approx Inductance |
|---|---|---|---|---|---|
| Small RF air coil | 10 | 12 | 8 | Wheeler single layer | 0.382 µH |
| General air coil | 25 | 40 | 20 | Wheeler single layer | 4.801 µH |
| Multilayer prototype | 20 | 25 | 80 | Wheeler multilayer | 77.656 µH |
| Longer solenoid | 50 | 80 | 60 | Long solenoid | 111.033 µH |
Formula Used
Wheeler single layer: L(µH) = r²N² / (9r + 10l). Here r and l are in inches.
Wheeler multilayer: L(µH) = 0.8r²N² / (6r + 9l + 10d). Here r, l, and d are in inches.
Long solenoid: L(H) = μ0 × μr × N² × A / l. Here dimensions are in meters.
The calculator accepts millimeters. It converts dimensions before calculation. Core permeability is applied as an approximate multiplier.
How to Use This Calculator
Choose the formula that matches your coil shape. Enter the inner diameter, coil length, turns, and layer count. Add wire diameter and core permeability. Set a frequency to calculate reactance. Press calculate. The result appears above the form. Use CSV or PDF buttons to save the calculation.
Coil Inductance Calculator Guide
A coil stores energy in a magnetic field. Its inductance depends on turns, diameter, length, core material, and winding depth. Millimeter inputs make the tool easy for bench work. You can enter measured coil sizes directly. The calculator then converts them before applying the selected equation.
Why millimeter inputs matter
Small RF coils are often built with calipers, mandrels, and enamel wire. These parts are normally measured in millimeters. Direct metric entry reduces mistakes. It also helps when comparing datasheets, winding notes, and prototype dimensions.
Advanced design checks
The calculator supports single layer, multilayer, and long solenoid estimates. It also estimates wire length, direct current resistance, inductive reactance, and a simple quality factor. These values help you judge heating, losses, and frequency behavior. The result is still an estimate. Real coils change with nearby metal, winding tension, insulation, shield cans, and lead length.
Choosing a formula
Use the single layer Wheeler equation for air core coils with one neat winding layer. Use the multilayer Wheeler equation when turns stack radially. Use the solenoid equation for longer coils where magnetic field assumptions are reasonable. A relative permeability field is included for core experiments. Treat high permeability results carefully, because cores can saturate and vary with frequency.
Practical winding tips
Keep leads short when testing RF coils. Measure the final wound length, not only the planned length. Count turns at the centerline of the wire. For close wound coils, wire diameter controls pitch. For spaced coils, measure the distance between turn centers. Use the export buttons to save the calculation record. This helps repeat the same winding later.
Reading the result
Inductance is shown in microhenries and millihenries. Reactance is calculated at the selected frequency. Resistance uses the chosen conductor resistivity and diameter. The quality factor is only a low frequency approximation. It does not include proximity effect, core loss, dielectric loss, or self resonance. For final products, confirm the coil with an LCR meter or network analyzer.
Accuracy limits
Calculator output is best for planning and comparison. It is not a replacement for measurement. Printed circuit coils, basket windings, ferrite rods, and toroids need special models. Use stable dimensions, then test under normal operating conditions when installed.
FAQs
1. What does this coil inductance calculator measure?
It estimates inductance from coil dimensions, turn count, winding style, and core permeability. It also estimates reactance, wire length, resistance, stored energy, and simple Q.
2. Can I enter all dimensions in millimeters?
Yes. The calculator accepts coil diameter, length, wire diameter, winding depth, spacing, and lead length in millimeters. It converts values internally for each formula.
3. Which formula should I select?
Use Wheeler single layer for one-layer air coils. Use Wheeler multilayer for stacked turns. Use long solenoid for long coils with a more uniform field.
4. Why is my measured coil different?
Nearby metal, lead length, turn spacing, insulation, winding pressure, and core behavior can change real inductance. Always verify final designs with a meter.
5. What is relative permeability?
Relative permeability describes how strongly a core supports magnetic flux compared with air. Air is about 1. Ferrite and iron cores can be much higher.
6. Does the Q value include all losses?
No. The Q estimate uses inductive reactance divided by DC resistance. It does not include skin effect resistance, proximity losses, dielectric losses, or core losses.
7. What does turn spacing do?
If turn spacing is above zero, the calculator uses it to estimate the effective coil length. Use zero when you want measured length instead.
8. Can this calculator design toroid coils?
No. Toroids need different magnetic path formulas. This tool is mainly for straight cylindrical coils, solenoids, and common Wheeler-style winding estimates.