Inductor Calculator Suite
A collection of tools for inductor design and analysis.
Air Core Inductor Calculator
This tool calculates the inductance of a single-layer, air-cored coil. The result is based on Wheeler's formula, which provides a good approximation for coils whose length is more than 0.4 times their diameter. Enter the coil's physical dimensions to see the calculated inductance.
D
l
Air Core Coil
Diagram shows coil diameter (D) and length (l).
Toroidal Inductor Calculator
Calculate the inductance of a wire-wound toroidal core. A toroid's shape confines the magnetic field well, making it an efficient inductor. You'll need the toroid's dimensions, the number of turns, and the relative permeability of the core material.
OD
ID
Diagram shows Toroid dimensions.
Inductor Color Code Calculator
Determine the value of an axial inductor by selecting the colors of its bands. Most common inductors use a 4-band system. Select the color for each band from the dropdowns to find the inductance and tolerance value.
Visual representation of the inductor.
Formulas & Theory
This section provides the formulas used in the calculators and brief explanations of the underlying principles. Understanding these formulas is key to effective inductor design and analysis.
Air Core Inductor (Wheeler's Formula)
L (µH) = (d² * n²) / (18d + 40l)
- L is the inductance in microhenries (µH).
- d is the coil diameter in inches.
- l is the coil length in inches.
- n is the number of turns.
- Note: Our calculator handles mm-to-inch conversion internally.
Toroidal Inductor
L (H) = (μ₀ * μᵣ * N² * h) / (2π) * ln(OD/ID)
- L is the inductance in Henries (H).
- μ₀Permeability of free space (~1.257×10⁻⁶ H/m) is the permeability of free space.
- μᵣThe material's ability to support a magnetic field. is the relative permeability of the core material.
- N is the number of turns.
- h is the height of the toroid in meters.
- OD and ID are the outer and inner diameters in meters.
- Note: Our calculator handles mm-to-meter conversion and result scaling.
Inductor Color Codes
The first two bands represent significant digits, the third is a decimal multiplier, and the fourth indicates tolerance.
| Color | Value (Bands 1 & 2) | Multiplier (Band 3) | Tolerance (Band 4) |
|---|---|---|---|
| Black | 0 | x1 | - |
| Brown | 1 | x10 | ± 1% |
| Red | 2 | x100 | ± 2% |
| Orange | 3 | x1k | ± 3% |
| Yellow | 4 | x10k | ± 4% |
| Gold | - | x0.1 | ± 5% |
| Silver | - | x0.01 | ± 10% |
| None | - | - | ± 20% |