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.
Inductor Q Factor Calculator
The Q factor (Quality Factor) represents the ratio of an inductor's reactance to its resistance at a given frequency. A higher Q factor indicates a more efficient inductor with less energy loss. Use this calculator to determine the Q factor for your component.
L
R
Diagram of an inductor with its series resistance.
Wire Self Inductance Calculator
This tool estimates the self-inductance of a straight, round wire. The inductance depends on the wire's length and diameter. The formula is an approximation that assumes a single, isolated wire in free space.
Diagram of a straight wire.
Parallel Wire Inductance Calculator
Calculate the inductance of two parallel, straight wires. This is useful for understanding the inductance of transmission lines or power bus configurations. The formula takes into account the wire diameter and the spacing between them.
Diagram of two parallel wires.
Coax Inductance Calculator
Calculate the inductance of a coaxial cable. The formula depends on the cable's length and the ratio of its outer and inner conductor radii. This is a crucial calculation for RF and high-frequency applications.
Diagram of a coaxial cable cross-section.
Single Circular Loop Inductance Calculator
Calculate the inductance of a single, isolated circular wire loop. This is a fundamental building block for many coil designs. The inductance is primarily a function of the loop's radius and the wire's radius.
Diagram of a single wire loop.
Mutual Inductance Calculator
Calculate the mutual inductance between two coupled inductors. This value indicates how much the magnetic field from one inductor affects the other. It's a key parameter for transformers and other coupled coil systems.
Diagram of two coupled inductors.
Inductor Energy Calculator
Calculate the amount of energy stored in an inductor's magnetic field. The energy is a function of the inductor's value and the current passing through it. This is a vital calculation for power electronics and energy storage applications.
Diagram of an inductor with current.
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.
Q Factor Formula
Q = (2π * f * L) / R
- Q is the Quality Factor (dimensionless).
- f is the frequency in Hertz (Hz).
- L is the inductance in Henries (H).
- R is the series resistance in Ohms (Ω).
Wire Self Inductance
L (H) = (μ₀ * l / 2π) * [ln(4l / d) - 1]
- L is the inductance in Henries (H).
- l is the wire length in meters.
- d is the wire diameter in meters.
- Note: Our calculator handles mm-to-meter conversion and result scaling.
Parallel Wire Inductance
L (H) = (μ₀ * l / π) * arccosh(D / d)
- L is the inductance in Henries (H).
- l is the wire length in meters.
- d is the wire diameter in meters.
- D is the distance between wire centers in meters.
- Note: Our calculator handles mm-to-meter conversion and result scaling.
Coax Inductance
L (H) = (μ₀ * l / 2π) * ln(b / a)
- L is the inductance in Henries (H).
- l is the cable length in meters.
- a is the inner conductor radius in meters.
- b is the outer conductor inner radius in meters.
- Note: Our calculator handles mm-to-meter conversion and result scaling.
Single Circular Loop Inductance
L (H) = μ₀ * r * [ln(8r / a) - 2]
- L is the inductance in Henries (H).
- r is the loop radius in meters.
- a is the wire radius in meters.
- Note: Our calculator handles mm-to-meter conversion and result scaling.
Mutual Inductance
M = k * sqrt(L₁ * L₂)
- M is the mutual inductance in the same unit as L₁ and L₂.
- k is the coupling coefficient (between 0 and 1).
- L₁ and L₂ are the self-inductances of the two coils.
Inductor Energy
E = 0.5 * L * I²
- E is the stored energy in Joules (J).
- L is the inductance in Henries (H).
- I is the current in Amperes (A).
- Note: Our calculator handles µH-to-H conversion.
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% |
