Calculator Inputs
Choose a method, enter known values, and calculate self inductance. Use μr = 1 for air-core coils.
Example data table
These sample cases show how different methods can produce self inductance values for coils and measured electrical behavior.
| Method | Example inputs | Calculated self inductance |
|---|---|---|
| Long solenoid | N = 300, radius = 1.2 cm, length = 18 cm, μr = 1 | 0.284245 mH |
| Toroid | N = 500, mean radius = 6 cm, area = 2.5 cm², μr = 1 | 0.208333 mH |
| Flux linkage | λ = 18 mWb-turn, I = 3 A | 6.000000 mH |
| Induced emf | e = 4.5 V, di/dt = 1200 A/s | 3.750000 mH |
| Energy | W = 0.09 J, I = 2 A | 45.000000 mH |
Formula used
Self inductance measures how strongly a coil opposes current change by inducing its own voltage. The calculator supports several physics-based methods.
- Long solenoid:
L = μ0 μr N² A / l, whereA = πr². - Toroid:
L = μ0 μr N² A / (2πrmean). - Flux linkage:
L = λ / I. - Induced emf:
L = |e| / |di/dt|. - Stored energy:
L = 2W / I².
Derived outputs include stored energy, reactance, flux linkage at a chosen current, time constant, and quality factor when resistance is supplied.
How to use this calculator
- Select the calculation method that matches your known data.
- Enter coil geometry, measured flux linkage, induced voltage, or stored energy values.
- Choose consistent units for length, area, and flux linkage.
- Enter target current, frequency, and resistance for extra derived outputs.
- Click Calculate Self Inductance to show the result above the form.
- Review the graph, compare outputs, and export the summary as CSV or PDF.
FAQs
1. What is self inductance?
Self inductance is a coil property that links changing current to induced voltage. A higher inductance means the coil resists current change more strongly.
2. Why does the number of turns matter so much?
Inductance usually scales with the square of turns. Doubling the turns can increase inductance by about four times when other coil dimensions stay unchanged.
3. When should I use the solenoid model?
Use the solenoid formula for long cylindrical coils where magnetic flux stays mostly inside the core and the winding length is much larger than the radius.
4. When should I use the toroid model?
Use the toroid model for ring-shaped magnetic paths. It works well when flux remains concentrated inside the toroidal core and leakage is relatively small.
5. Does frequency change inductance?
Ideal inductance is a physical property of the coil and core. Frequency changes reactance, not the base inductance value, unless material behavior shifts with frequency.
6. What does relative permeability do?
Relative permeability shows how strongly a core material supports magnetic flux compared with free space. Higher permeability usually increases inductance for the same geometry.
7. Why are there several methods in one calculator?
Engineers and students often know different quantities. Geometry works in design, while flux linkage, induced voltage, or energy methods fit measurement and lab problems.
8. What units are most common for inductance?
The SI unit is the henry. Real coils are often reported in millihenry, microhenry, or nanohenry because many practical values are much smaller than one henry.