Estimate key coil properties from wire diameter, winding count, and bobbin dimensions. Review coil geometry, wire length, resistance, and rated-current performance in one place.
Coil Parameters
Results
Introduction
What is an Electric Coil?
An electric coil (also known as an electromagnetic coil) is a fundamental electrical component consisting of conductive wire wrapped around a core. The core can be ferromagnetic (like iron or steel) to amplify the magnetic field, or it can be air/non-magnetic for specific applications.
How it Works:
When electric current flows through the wire, it generates a magnetic field around the coil. This interaction allows coils to perform three main functions:
Inductance: Resisting changes in current flow.
Electromagnetism: Creating a magnetic force to move objects (e.g., in motors or solenoids).
Induction: Transferring energy between circuits (e.g., in transformers).
Types of Electrical Coils
Coils are categorized based on their core material, winding shape, and function. Below are the most common types used in electronics and engineering.
1. Structural & Core Variations
Bobbin Wound Coils: The wire is wound onto a plastic "bobbin" or spool. This is common for relays and sensors where the coil needs a rigid structure.
Toroidal Coils: Wire is wound around a donut-shaped (ring) core. This shape confines the magnetic field within the core, preventing leakage and interference with nearby components.
Air Core / Self-Supported Coils: Used when a magnetic core is undesirable (e.g., high-frequency radio circuits) or space is limited. The wire is stiff enough to hold its own shape.
2. Functional Variations
Choke Coils: Designed specifically to block (choke) high-frequency Alternating Current (AC) while letting Direct Current (DC) pass through.
Solenoid Coils: These convert electrical energy into linear motion. When energized, the magnetic field pulls a metal plunger inside the coil.
Tesla Coils: A resonant transformer circuit used to produce high-voltage, low-current, high-frequency alternating-current electricity.
Transformer Coils: Used in pairs (primary and secondary) to step voltage up or down via electromagnetic induction.
Coil Formulas & Calculations
To design a coil, you must calculate physical properties like wire length, resistance, and the number of turns.
Key Variables:
N: Number of turns
d: Wire Diameter
Dbobbin: Diameter of the Bobbin (Inner Diameter)
Lbobbin: Length of the Bobbin
Dcoil: Outer Diameter of the finished coil
Common Formulas
1. Cross-Sectional Area of Wire (A)A=π×r2(Where r is the radius of the wire)
2. Radius of Middle of Coil (rmid)
Used to calculate the average length of one turn.
rmid=2(N×d)+Dbobbin
3. Total Wire Length (Ltotal)Ltotal=2×π×rmid×N
4. Electrical Power (P)P=V×I(Where V is Voltage and I is Current)
5. Ohm's Law (Voltage & Resistance)V=R×I
How to Calculate Coil Properties
1. Calculating Number of Turns
The number of turns (N) is critical for determining the strength of the magnetic field.
By Dimensions: If you know the bobbin length (Lbobbin) and wire diameter (d), the turns per layer is roughly Lbobbin/d. Multiply this by the number of layers.
By Voltage (Transformers): The formula is derived from the core's magnetic flux:
TurnsPerVolt=4.44×F×M×A
.
2. Calculating Inductance
Inductance (L) measures the coil's ability to store energy. For a simple air-core coil, the approximation is:
L(μH)=18d+40ld2×N2(Where d is coil diameter in inches and l is coil length in inches).
AWG Wire Gauge Chart
Use this chart to determine the resistance and diameter of copper wire for your coil. Thicker wire (lower AWG) handles more current but takes up more space.
AWG
Diameter (mm)
Resistance (Ω/m)
AWG
Diameter (mm)
Resistance (Ω/m)
4/0
11.7
0.000161
22
0.644
0.0530
3/0
10.4
0.000203
23
0.573
0.0668
2/0
9.26
0.000256
24
0.511
0.0842
1/0
8.25
0.000323
25
0.455
0.106
1
7.35
0.000407
26
0.405
0.134
2
6.54
0.000513
27
0.361
0.169
3
5.83
0.000647
28
0.321
0.213
4
5.19
0.000815
29
0.286
0.268
5
4.62
0.00103
30
0.255
0.339
6
4.11
0.00130
31
0.227
0.427
7
3.66
0.00163
32
0.202
0.538
8
3.26
0.00206
33
0.180
0.679
9
2.91
0.00260
34
0.160
0.856
10
2.59
0.00328
35
0.143
1.08
11
2.30
0.00413
36
0.127
1.36
12
2.05
0.00521
37
0.113
1.72
13
1.83
0.00657
38
0.101
2.16
14
1.63
0.00829
39
0.0897
2.73
15
1.45
0.0104
40
0.0799
3.44
16
1.29
0.0132
41
0.0711
4.34
17
1.15
0.0166
42
0.0633
5.47
18
1.02
0.0210
43
0.0564
6.90
19
0.912
0.0264
44
0.0502
8.70
20
0.812
0.0333
45
0.0447
10.98
21
0.723
0.0420
FAQ
How does wire thickness impact coil performance?
Thinner wire increases resistance per meter, which raises copper loss and heat for a given current. Thicker wire lowers resistance but reduces the number of turns that fit in the same winding area. This calculator adjusts resistance and winding geometry based on the wire diameter you enter.
What is the purpose of the "Rated DC Current" field?
This optional input lets the calculator determine the DC voltage needed using V = I × R and the power dissipation using P = I² × R. It helps designers evaluate thermal conditions and confirm whether the coil can operate safely under continuous current without overheating.
How is total wire length calculated for a coil?
Total wire length is based on the average winding diameter and the number of turns. The calculator uses L = 2 × π × r_mid × N, where r_mid = ((N × d) + D_bobbin) / 2. This represents the middle-layer diameter and assumes a uniform, single-layer winding density.
Why does the calculator exclude core material properties?
This tool focuses on air-core coils and single-layer windings. Cores made of iron or ferrite introduce permeability, saturation, hysteresis, and eddy-current losses that require more advanced simulation tools and core-specific material data, which are beyond the scope of this calculator.
(Where F = Frequency, M = Magnetic Flux, Acore = Core Area)
Op-Amp Voltage and Gain Calculator
86
Calculate output voltage together with inverting and non-inverting gain for operational-amplifier circuits. Enter V1, V2, Vp, Vn, and resistor values R1 through R4 to obtain accurate results for circuit design, troubleshooting, and op-amp learning.
