How to Convert American Wire Gauge (AWG) to Wire Sizes in mm²

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Understanding the relationship between wire gauge numbers (AWG) and their equivalent sizes in square millimeters (mm²) is essential for safe and efficient electrical work. The American Wire Gauge (AWG) system is widely used in the US, while mm² is the standard measurement in many other countries. This guide provides a clear comparison between these two systems, ensuring you select the correct wire size for your electrical projects.

Whether you work locally or sometimes you are involved in projects internationally, the ability to convert from AWG to mm² greatly simplifies your work and ensure that your language is global and universal if you are working with a team from different regions around the globe

American Wire Gauge (AWG)  to mm² Conversion Table

AWG (Gauge Number)	Diameter (mm)	Cross-Sectional Area (mm²)
0000 (4/0)	11.68	107.22
000 (3/0)	10.40	85.03
00 (2/0)	9.27	67.43
0 (1/0)	8.25	53.49
1	7.35	42.41
2	6.54	33.62
3	5.83	26.67
4	5.19	21.15
5	4.62	16.77
6	4.11	13.30
7	3.67	10.55
8	3.26	8.37
9	2.91	6.63
10	2.59	5.26
12	2.05	3.31
14	1.63	2.08
16	1.29	1.31
18	1.02	0.823
20	0.81	0.517
22	0.64	0.326
24	0.51	0.205
26	0.40	0.129
28	0.32	0.0810
30	0.25	0.0509

How to Use This Table

1. Identify the AWG Size:

·       Check the wire’s insulation or refer to its specifications to determine its AWG number.

2. Match AWG to mm²:

·       Use the table above to find the corresponding size in square millimeters (mm²).

3. Ensure Compatibility:

·       Verify that the selected wire size meets the requirements for the intended electrical load and complies with local codes.

Why Converting Wire Sizes Matters

• Global Compatibility: Electrical projects often require adherence to international standards, and knowing both AWG and mm² measurements ensures seamless integration.
• Safety Assurance: Choosing the correct wire size minimizes the risk of overheating, voltage drops, or fire hazards.
• Efficiency: Proper wire sizing reduces energy losses and ensures the longevity of your electrical system.

Practical Applications of AWG to mm² Conversion

• DIY Projects: Homeowners working on minor electrical repairs or upgrades.
• International Standards: Engineers and contractors managing projects that involve both AWG and mm² specifications.
• Troubleshooting: Quickly identifying and replacing wires in mixed-standard systems.

Understanding the conversion between wire gauge numbers and mm² sizes is crucial for anyone involved in electrical work, whether it’s for residential, commercial, or industrial projects. Use this guide as a quick reference to ensure your wiring projects meet safety and performance standards.

How to Calculate the Inductance of an Electric Cable

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The inductance, L , per core of a 3-core cable or of three single-core cables comprises two parts namely the self-inductance of the conductor and the mutual inductance with other cores. 

The formula for calculating the Inductance of a cable is given by:

$L = K + 0.2Log_e{\frac{2S}{d}}$                    (Hm/Km)

Where:
L  =  Inductance of cable in (Hm/Km)

K  =  a constant relating to the conductor formation (see table below)

S  =  axial spacing between conductors within the cable (mm) or axial spacing between 

       Conductors of a trefoil group of single core cables (mm) or 

   =  1.26 x phase spacing for a flat formation of three single-core cables (mm)

d =  conductor diameter or for shaped designs the diameter of an equivalent circular     

        conductor (mm)

For 2-core, 3-core and 4-core cables, the inductance obtained from the formula should be multiplied by 1.02 if the conductors are circular or sector-shaped, and by 0.97 for 3-core oval conductors.

Typical Values for K for Different Stranded Conductors (at 50Hz)

Number of Wires in Conductor	K
3	0.0778
9	0.0642
7	0.0554
37	0.0528
61 and Over	0.0514
1 (Solid)	0.0500
Hollow core conductor, 12mm duct	0.0383

Electrical and Physical Properties of Common Metals Used in Manufacturing Cables

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The tables below indicate the electrical and physical properties of metals commonly used in the manufacture of electric cables in the electrical industry. Familiarity with these properties is required to fully grasp the key advantages and disadvantages of the various materials used and to understand from a practical standpoint why they are applied in the area they are used.

Electrical Properties

The table below indicates the electrical properties of the common metals used in cables. Taking price into consideration the below listed properties, Copper and Aluminium are clearly the best choice for conductors the manufacture of all manner of electric cables although there has been experimentation with other metals for example Sodium in certain applications:

Metals	Relative Conductivity (Copper = 100)	Electrical Resistivity at 20°C (Ωm, 10-8)	Temperature Coefficient of Resistance (per °C)
Silver	106	1.626	0.0041
Copper (HC, anealed)	100	1.724	0.0039
Copper (HC, Hard drawn)	97	1.777	0.0039
Tinned Copper	95 - 99	1.741 - 1.814	0.0039
Aluminium (EC grade, Soft)	61	2.803	0.0040
Aluminium (EC grade,         1/2H - H)	61	2.826	0.0040
Sodium	35	4.926	0.0054
Mild Steel	12	13.80	0.0045
Lead	8	21.4	0.0040

Physical Properties of Metals Used in Electric Cables
The physical properties of metals used for conductors and sheaths are given in the table below:

Property	Unit	Aluminium	Copper	Lead
Density at 20°C	Kg/m3	8890	2703	11370
Coefficient of thermal expansion per °C	x 10-6	17	23	29
Melting point	oC	1083	659	327
Thermal Conductivity	W/cm oC	3.8	2.4	0.34
Ultimate Tensile Stress
Soft temper	MN/m2	225	70 - 90	-
3/4H to H	MN/m2	385	125 - 205	-
Elastic Modulus	MN/m2	26	14	-
Hardness
Soft	DPHN	50	20 - 25	5
3/4H to H	DPHN	115	30 - 40	-
Stress Fatigue Endurance Limit (Approximate)	MN/m2	±65	±40	±2.8

Except for conductors of self-supporting overhead cables, Copper is invariably used in the annealed condition. Solid Aluminium conductors are also mainly used in a soft condition but stranded Aluminium conductors are 3H (hard) to H. Aluminium sheaths are now extruded directly onto cables and hence of soft temper but a small amount of work hardening occurs during corrugation.

Basics of Coaxial Cables Used in Electronic and Computer Systems

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A coaxial cable consists of four basic parts:

• Inner conductor (center conductor)
• Outer conductor (shield)
• Dielectric, which separates the inner and outer conductors
• Jacket, which is the outer polymer layer protecting the parts inside

Parts of a Typical Coaxial Cable Photo Credit : ANIXTER CABLES

The following characteristics/properties help to define a coaxial cable as applied in electronic systems and Computer Systems:

1. Characteristic impedance

2. Voltage Standing-Wave Ratio (VSWR)

3. Velocity of Propagation

4. Voltage Rating

5. Operating Temperature

Characteristic Impedance

The characteristic impedance of a coaxial cable is a function of its geometry and materials. Characteristic impedance is independent of length and typically ranges from 35 to 185 ohms. The most common values are 50, 75 and 93 ohms. The characteristic impedance of a cable is not the same as the  impedance of the conductors in a cable, which is dependent on length.

The most efficient transfer of energy from a source to a load occurs when all parts of the system have the same characteristic impedance. To have better performance with coaxial cable, there is need for impedance matching especially critical at higher frequencies, where the consequences of mismatches are more severe.

Voltage Standing - Wave Ratio (VSWR)

The voltage standing-wave ratio (VSWR) is a measure of the standing waves that result from reflections. It expresses the uniformity or quality of a cable’s characteristic impedance. Uniformity is also measured as structural return loss (SRL).

Velocity of Propagation

Velocity of propagation is the speed at which electromagnetic energy travels along the cable. In free space or air, electromagnetic energy travels at the speed of light, which is 186,000 miles per second. In other materials, however, the energy travels slower, depending on the dielectric constant of the material. Velocity of propagation is expressed as a percentage of the speed of light. For example, a velocity of 65 percent means that the energy travels at 120,900 miles per second – or 35 percent slower than in free space. The dielectric (insulation) separating the two conductors determines the velocity of propagation. Although the electromagnetic energy travels in the dielectric, the current associated with the energy travels primarily on the outside of the center conductor and the inside of the outer conductor (shield).

The two conductors bind the energy within the cable. Consequently, the quality of the dielectric is important to efficient, speedy transfer of energy. Speed is important to engineers who must know the transit time of signals for digital transmission.

Voltage Rating

This is the maximum voltage the cable is designed to handle.

Operating Temperature Range

These are the minimum and maximum temperatures at which the cable can operate.

Types of Coaxial Cables

There are many types of coaxial cables but four types are commonly used namely:

1. Flexible Coax

2. Semirigid Coax

3. Triaxial 

4. Dual Coax

There is also Twinaxial (Twinax) Cable used in high-speed, balanced-mode multiplexed transmission in large computer systems.

Flexible Coax

The most common type, flexible coax has a braided outer conductor (shield) of extremely fine wires. While the braid makes the cable flexible, it does not provide complete shielding – energy (RF signals) can leak through the shield via minute gaps in the braid. To combat this, many cables have several layers in the outer conductor. In addition, thin foils are sometimes used to supplement the braid to provide better coverage for greater shielding effectiveness. The greater the coverage, the better the shield

Semirigid Coax

Semirigid coax has a solid, tubular metallic outer conductor, similar to a pipe. This construction gives the cable a very uniform characteristic impedance (low VSWR) and excellent shielding, but at the expense of flexibility.

Triaxial Cable (Triax)

This coax has two outer conductors (shields) separated by a dielectric layer. One outer conductor (shield) serves as a signal ground, while the other serves as earth ground, providing better noise immunity and shielding. One caution: Do not confuse a flexible cable having a multilayer outer shield with triaxial cable.

Dual Coax

This cable contains two individual coaxial cables surrounded by a common outer jacket.

Shown below are the four basic types of coaxial cables commonly used

Common Types of Coaxial Cables - Photo Credit : ANIXTER CABLES

Twinaxial Cable (Twinax)

Twinax has a pair of insulated conductors encased in a common outer conductor (shield). The center conductors may be either twisted or run parallel to one another. In appearance, the cable is often like a shielded twisted pair, but it is held to the tighter tolerances common to fixed-impedance coaxial cable. A common use of twinax is high-speed, balanced-mode multiplexed transmission in large computer systems. Balanced mode means that the signal is carried on both conductors, which provides greater noise immunity.

A Typical Twinaxial Cable - Photo Credit: ANIXTER CABLE

Resistance and Reactance per km of Copper and Aluminium cables

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For the purpose of calculating voltage drop within a cable, the table below gives the reactance and resistance values for Copper and Aluminium cables:

Values for Copper Cables

Cable Size, S (mm2)	Single - Core Cable		Two - Core/Three Core Cables
	R(Ω/km) @ 80°C	X (Ω/km) @ 80°C	R(Ω/km) @ 80°C	X(Ω/km) @ 80°C
1.5	14.8	0.168	15.1	0.118
2.5	8.91	0.156	9.08	0.109
4	5.57	0.143	5.68	0.101
6	3.71	0.135	3.78	0.0955
10	2.24	0.119	2.27	0.0861
16	1.41	0.112	1.43	0.0817
25	0.889	0.106	0.907	0.0813
35	0.641	0.101	0.654	0.0783
50	0.473	0.101	0.483	0.0779
70	0.328	0.0965	0.334	0.0751
95	0.326	0.0975	0.241	0.0762
120	0.188	0.0939	0.191	0.074
150	0.153	0.0928	0.157	0.0745
185	0.123	0.0908	0.125	0.0742
240	0.0943	0.0902	0.0966	0.0752
300	0.0761	0.0895	0.078	0.075

Values for

Ampacity Correction Factors for All Cables

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As already discussed in Ampacity of a Conductor, the ampacity of a conductor depends on temperature. Any change in ambient temperature affects the ampacity of an electrical cable. When this happens, correction factors are applied to get new ratings for such a conductor.
The approximate ampacity correction factors for all cables under different ambient temperature conditions for cables whose insulation is rated 90 degree C are given below:

Thermal Properties of Cable Polymers

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Often times in the application of electrical cables, we neglect the thermal characteristics of  the polymers used in the cable insulation. Here is a list of the temperature range each of the common electrical cable polymers can withstand while in service or operation:

How to Calculate Conductor Diameter from Wire Diameter

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To calculate the nominal diameter of any concentric-lay-stranded conductor made from round wires of uniform diameters, multiply the diameter of an individual wire by the applicable factors listed below:

How to Determine Temperature Correction Factors for Resistance: Copper Conductors

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The DC resistance of copper wire increases with increasing temperature in accordance with the formula:

On the basis of the above formula, we now generate a table of correction factors for copper conductors in operating in the temperature range 25 – 200 degree celsius:

NEMA Insulation Classes for Transformers

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The capacity or rating of a transformer is limited by the temperature that the insulation can tolerate.  The life of a transformer can be extended by making sure it is not operated over and above the temperature rating of the insulation system on a continuous basis. A guiding rule of thumb would be that the useful operating life of the transformer halves for every 10°C  rise above its rated temperature. 

The insulation system of a transformer is rated in degrees Celsius at its maximum temperature rating:

The class number  = the maximum °C of the transformer insulation

NEMA (National Manufacturer’s Association) has the following thermal or insulation classification as regards transformers (dry type):

Ampacity of a Conductor

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Ampacity is the current carrying capacity of a conductor. Ampacity calculation should take into account natural variables such as solar warming, wind and air density, viscosity, and thermal conductivity. Ampacity is a temperature rating. In order words, as temperature changes, the ampacity of a conductor changes. 

Increase in ambient/surrounding/medium temperature can significantly limit the current carrying capacities of cables. As cable temperature increases, its resistance increases thereby reducing the amount of current that can be carried. 

According to the National Electrical Code, article 310.15(C), the ampacities of conductors can be calculated by the following general formula:

AC Resistance of a Conductor

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A conductor offers a greater resistance to the flow of alternating current(AC) than it does to direct current(DC). The magnitude of the increase is usually expressed as an “AC/DC ” ratio. The reasons for the increase include:

1. Skin effect, 
2. Proximity effect, 
3. Hysteresis and eddy current losses in nearby ferromagnetic materials, and
4. Induced losses in short-circuited nearby non-ferromagnetic materials

Skin Effect

Skin Effect describes the phenomena of alternating current flowing more densely near the surface of a conductor. The net effect is a reduction in effective area and an increase in the resistance. To calculate skin effect in tubular conductors made of solid wire to an infinitely thin tube, the curves of Ewan are used.

The parameter is:

DC Resistance of a Conductor

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The DC resistance of a conductor or cable is that defined by ohms law. It is a function of many factors including temperature which greatly affects the resistance of a given material. Copper and Aluminium are the most widely used conductors. Their resistance (DC) increases with increasing temperature. 

The DC resistance of copper wire at 20 degree Celsius(68 degree Fahrenheit) is given below:

American Wire Gauge (AWG)

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Wire size is expressed in circular mils(CM). A mil is one-thousandth of an inch. In the United States, the American Wire Gauge is used. It is a scale of even numbers that start with the number 40 and descend. The cross-sectional area becomes larger as the numbers on this scale get smaller. 

For wires larger than No.2 wire, a scale of 1/0, 2/0, 3/0 and 4/0 is used. For even larger wires, thousands of circular mils is used –MCM or Kcmil

AWG Conversions

Copper conductor size conversions are determined using;

Circular mils = sq in. x 1,273,240 = sq mm x 1,973.5

For conductor cross-sectional forms other than circular, where S is the cross-sectional area in square inches, the conversions are:

ELECTRICAL CONDUCTORS AND INSULATORS

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Electrical Conductors:

The most popular electrical conductors are Copper and Aluminum.

Copper is the popular choice for power distribution and control circuits because of its excellent ability to conduct electric current as well as other electrical and mechanical properties. Copper may be coated with Tin, Nickel or Silver to ensure easier soldering and to retard corrosion

Aluminium is also used in power applications. Its principal advantages are its weight and lower material cost when compared with copper.

The main disadvantages of Aluminium are :

(a) It has a lower conductivity than Copper hence it will require larger wire and cable sizes than Copper

(b) Aluminium oxidizes quickly when exposed to air. This oxidation acts as an insulator. This creates additional cost with regard to maintenance and testing when compared to Copper

Aluminium is widely used by the electric utilities in overhead lines primarily because of its light weight and cost when compared to copper.

CALCULATION OF CABLE RESISTANCE

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Consider an example using the reistance formula:-
A copper conductor of length 500 meters is used to supply electrical energy to a lighting load of 1,000W. If the cross sectional area of the conductor is 10mmsq, calculate the resistance of the conductor. If the copper conductor were replaced with an Aluminium conductor of the same length, calculate the resistance of the Aluminium conductor.
Solution:
The resistance per km for copper is given by:

ELECTRICAL RESISTANCE

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ELECTRICAL RESISTANCE:
Electrical resistance is the opposition of a given material to the flow of electricity. The resistance of a an electric conductor is given by the formula:

R = eL/A
Where R = Resistance in ohms
            L = Length in meters
            A = Cross sectional area of conductor (c.s.a)
            e =  Resistivity of the conductor in ohms meter


Resistivity e = RA/L
If A = 1msq, then: resistivity is defined as the resistance per meter for a unit c.s.a
The two most popular conductors encountered in the electrical engineering field are Copper and Aluminium

The electrical resistance of a conductor is dependent on the following factors:
(a) temperature
(b) length of conductor material
(c) cross sectional area (c.s.a) of conductor

OHM'S LAW:
Ohm's law states that the voltage applied across a conductor is directly proportional to the current passing through the conductor provided the temperature and physical condition of the conductor remains constant.

This implies that:
V = IR
Where V = Voltage applied across conductor
            I  = Current passing through the conductor
           R  = Resistance of conductor

For direct current systems, resistance is the appropriate term to use. For alternating current systems, impedance is the right term to use. Impedance is the opposition to the flow of alternating current through a conductor. Impedance is as a result of resistive, capacitive and inductive effect of alternating current on the conductor. For small sizes of conductor, the capacitive and inductive effects due to alternating current is usually negligible and the term resistance could be used

Often in electrical works, there is the need to determine approximately the resistance of a conductor.
Resistance in ohms per km is given by:
R = (22.5 Ohms mmsq)/S(c.s.a) per km for Copper

R = (36 Ohms mmsq)/S(c.s.a) for Aluminium
Inductive reactance is negligible for conductors of c.s.a less than 50mmsq