Calculated Ind – Loan calculator

Air-Core Inductance Calculator

Use this calculator to estimate the inductance of a single-layer air-core coil. This approximation is widely used for RF coils where the coil length is at least 0.4 times the coil diameter.

Number of Turns (N):

Coil Diameter (D) in mm:

Coil Length (l) in mm:

function calculateInductance() { var numTurns = parseFloat(document.getElementById("numTurns").value); var coilDiameterMM = parseFloat(document.getElementById("coilDiameter").value); var coilLengthMM = parseFloat(document.getElementById("coilLength").value); var resultDiv = document.getElementById("inductanceResult"); // Input validation if (isNaN(numTurns) || numTurns 0)."; return; } if (isNaN(coilDiameterMM) || coilDiameterMM 0)."; return; } if (isNaN(coilLengthMM) || coilLengthMM 0)."; return; } // Convert mm to inches for the formula var coilDiameterInches = coilDiameterMM / 25.4; var coilLengthInches = coilLengthMM / 25.4; // Formula for single-layer air-core coil inductance (Wheeler's formula approximation) // L (µH) = (N^2 * D_inches^2) / (18 * D_inches + 40 * l_inches) var numerator = numTurns * numTurns * coilDiameterInches * coilDiameterInches; var denominator = (18 * coilDiameterInches) + (40 * coilLengthInches); if (denominator === 0) { resultDiv.innerHTML = "Cannot calculate: Denominator is zero. Check input values."; return; } var inductanceMicroHenries = numerator / denominator; resultDiv.innerHTML = "

Calculated Inductance:

" + "The estimated inductance of your coil is: " + inductanceMicroHenries.toFixed(4) + " µH"; } .calculator-container { font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif; background-color: #f9f9f9; padding: 25px; border-radius: 10px; box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1); max-width: 600px; margin: 30px auto; border: 1px solid #e0e0e0; } .calculator-container h2 { color: #333; text-align: center; margin-bottom: 20px; font-size: 1.8em; } .calculator-container p { color: #555; line-height: 1.6; margin-bottom: 15px; } .calc-input-group { margin-bottom: 18px; display: flex; flex-direction: column; } .calc-input-group label { margin-bottom: 8px; color: #333; font-weight: bold; font-size: 1.05em; } .calc-input-group input[type="number"] { padding: 12px; border: 1px solid #ccc; border-radius: 6px; font-size: 1em; width: 100%; box-sizing: border-box; transition: border-color 0.3s ease; } .calc-input-group input[type="number"]:focus { border-color: #007bff; outline: none; box-shadow: 0 0 5px rgba(0, 123, 255, 0.3); } .calc-button { background-color: #007bff; color: white; padding: 14px 25px; border: none; border-radius: 6px; cursor: pointer; font-size: 1.1em; font-weight: bold; display: block; width: 100%; margin-top: 25px; transition: background-color 0.3s ease, transform 0.2s ease; } .calc-button:hover { background-color: #0056b3; transform: translateY(-2px); } .calc-button:active { background-color: #004085; transform: translateY(0); } .calc-result { margin-top: 30px; padding: 20px; background-color: #e9f7ff; border: 1px solid #b3e0ff; border-radius: 8px; text-align: center; font-size: 1.15em; color: #0056b3; } .calc-result h3 { color: #004085; margin-top: 0; margin-bottom: 10px; font-size: 1.4em; } .calc-result p { margin: 0; color: #0056b3; } .calc-result p.error { color: #dc3545; font-weight: bold; }

Understanding Inductance and Air-Core Coils

Inductance is a fundamental property of an electrical conductor that opposes changes in electric current. When current flows through a coil, it generates a magnetic field. If the current changes, the magnetic field also changes, inducing a voltage across the coil that opposes the change in current. This property is called inductance, and it's measured in Henries (H), though microhenries (µH) are more common for smaller coils.

What is an Air-Core Coil?

An air-core coil is an inductor that does not use a ferromagnetic material (like iron or ferrite) as its core. Instead, its core is simply air or another non-magnetic material like plastic or ceramic. These coils are commonly used in high-frequency (RF) applications because they avoid the energy losses and non-linearities associated with magnetic cores, such as hysteresis and saturation. While they offer lower inductance values compared to coils with magnetic cores for the same number of turns, their predictable behavior and stability at high frequencies make them invaluable.

Why Calculate Inductance?

Calculating the inductance of an air-core coil is crucial in various electronic design scenarios:

RF Circuit Design: Inductors are key components in resonant circuits (LC tanks), filters, and impedance matching networks in radio frequency applications. Knowing the inductance allows engineers to design circuits that operate at specific frequencies.
Antenna Design: Loading coils in antennas can be used to electrically lengthen a physically short antenna, and their inductance needs to be precisely calculated.
Prototyping: Before winding a physical coil, calculating its approximate inductance helps in determining the number of turns, wire gauge, and coil dimensions needed to achieve a desired inductance value.
Troubleshooting: Comparing calculated inductance with measured values can help identify manufacturing defects or design discrepancies.

Factors Affecting Inductance

The inductance of an air-core coil is primarily determined by its physical dimensions and the number of turns:

Number of Turns (N): Inductance is proportional to the square of the number of turns. Doubling the turns quadruples the inductance.
Coil Diameter (D): Larger coil diameters generally lead to higher inductance, as they encompass a larger magnetic field area.
Coil Length (l): The length of the coil affects how tightly packed the turns are. For a given number of turns, a shorter coil (more tightly packed) will have higher inductance than a longer, more spread-out coil.
Wire Spacing: While not a direct input in this simplified calculator, the spacing between turns also plays a role. Tightly wound coils have higher inductance.

The Formula Used

This calculator uses a common approximation known as Wheeler's formula for single-layer air-core coils. The formula is:

L (µH) = (N² * D²) / (18 * D + 40 * l)

Where:

L is the inductance in microhenries (µH)
N is the number of turns
D is the coil diameter in inches
l is the coil length in inches

It's important to note that this formula is an approximation and works best when the coil length (l) is at least 0.4 times the coil diameter (D). For very short or very long coils, more complex formulas or simulation tools might be necessary for higher accuracy.

How to Use the Calculator

Number of Turns (N): Enter the total number of times the wire is wound around the coil form.
Coil Diameter (D) in mm: Input the outer diameter of the coil in millimeters.
Coil Length (l) in mm: Enter the length of the wound section of the coil in millimeters.
Click "Calculate Inductance" to see the estimated inductance in microhenries (µH).

Examples of Inductance Calculation

Let's look at some practical examples:

Example 1: Small RF Choke
- Number of Turns (N): 15
- Coil Diameter (D): 5 mm
- Coil Length (l): 8 mm
- Calculated Inductance: Approximately 0.35 µH
Example 2: Medium Inductor for a Filter
- Number of Turns (N): 30
- Coil Diameter (D): 10 mm
- Coil Length (l): 15 mm
- Calculated Inductance: Approximately 2.5 µH
Example 3: Larger Coil for a Tuner
- Number of Turns (N): 50
- Coil Diameter (D): 25 mm
- Coil Length (l): 30 mm
- Calculated Inductance: Approximately 15.7 µH

These examples demonstrate how varying the physical parameters significantly impacts the resulting inductance. This calculator provides a quick and easy way to estimate these values for your projects.