Demystifying AWG: Essential Guide to Understanding Wire Sizes

Written by Dave Harris, trueCABLE Technical Specialist, BICSI INST1, INSTC Certified

Have you ever wondered what is meant when someone mentions the “gauge” of a wire? Maybe you’ve been told that you need 12-gauge wire or No. 12 AWG for an electrical installation. (“12-gauge wire” and “No. 12 AWG” mean the same thing.) That number “12” is an indicator of the diameter of a wire, as defined in the American Wire Gauge standard specification. Communication about wire sizes is crucial to the design of electrical installations. Because wire size is related to electrical resistance, it is important to both the performance and safety of any electrical system.

The American Wire Gauge

The American Wire Gauge (AWG) system for quantitatively describing the diameters and cross-sectional areas of solid round wires has been in place since the year 1857. The cross-sectional area can be used to calculate ampacity (current-carrying capacity), resistance, and strength, depending on the properties of the metal used in the wire.

When the AWG started, it was based on the number of drawing operations used to obtain the desired thickness of wire. Thinner wires required more drawing operations and were therefore assigned larger gauge numbers than larger wires that required fewer drawing operations. So, the larger the AWG number, the smaller the diameter of the wire. This makes the American Wire Gauge an example of an inverse gauge. 

AWG and Ethernet Installations

If you’ve spent much time with Ethernet cable, you might have noticed that our Cat5e cable contains No. 24 AWG solid copper conductors, and that our Cat6A cable uses No. 23 AWG solid copper conductors. 24 is a greater number than 23. Shouldn’t the higher Category cable have the bigger wires? Usually yes, and Cat6A cable does have larger conductors, despite the fact that the AWG number is smaller for the wire used in Cat6A cable. 

 When it comes to patch cords, wire sizes are generally smaller for all cable Categories, but their AWG numbers are larger (24, 26, or 28). Again, this is because in the American Wire Gauge system, larger numbers equate to smaller wires.

AWG and Electrical Installations

AWG wire size is crucial for electrical installations. This is because the cross-sectional area of a wire, along with the length and resistivity can be used to determine the resistance of a wire. The resistivity is a property of the metal used to make the wire. The resistance can be used to predict how much electrical current the wire can transmit safely and efficiently. So when electricians choose a certain gauge of a certain type of wire, they can predict the number and types of devices that can be installed on a particular electrical wire circuit. They can also determine the maximum amount of current that the wire is designed to carry, so that suitable fuses or circuit breakers can be chosen to protect the circuit and the structure.

More about AWG and Ethernet Cable

Since the size of a wire affects its resistance over distance, AWG wire size also affects the maximum allowable length for an Ethernet channel. Since a typical Ethernet channel is partially composed of patch cables, wire size is also an important consideration when choosing patch cables.

According to TIA standards, the maximum length for an Ethernet channel over copper twisted-pair cable at 68°F is 100 meters, or 328 feet, including patch cables. The maximum distance for the permanent link (the part without patch cables) is 90 meters or 95 feet. But this is only if the patch cables are constructed using No. 24 AWG wire. If smaller wire is used for patch cables, the maximum allowable lengths for both the permanent link and the patch cable are reduced or “derated.” The maximum allowable length for a patch cord made from No. AWG 28 wire is 15 meters, or 49 feet. That’s true even if the patch cable makes up the entire Ethernet channel. You can read more about wire sizes and Ethernet channel length in our Cable Academy blog article, “Maximum Ethernet Cable Length.”

Bonding and grounding are important in Ethernet installations as well as electrical installations. Whether you are grounding a shielded patch panel, a lightning arrestor, or an entire telecommunications room, the choice of wire sizes for the ground system affects not only safety, but the correct operation of every device on the network. For example, our shielded patch panel requires at least a No. 14 AWG stranded wire for bonding to ground. There’s more about grounding and bonding in, “Residential Bonding and Grounding of Shielded Ethernet Cable Systems” and “Commercial Bonding and Grounding of Ethernet Cable Systems.”

Table of Standard Diameters

Currently, the American Wire Gauge standard is maintained by ASTM International, and the designation for the standard is ASTM B258-18. The values for the diameters and cross-sectional areas for standard wires are given in Table 1. Wire sizes 46 to 56 AWG are generally finer than a human hair and are not reliably measured using a standard micrometer. They are not included in some published AWG tables, but we include them here because they might have value to some readers.

Table 1. Standard Diameters and Cross-Sectional Areas of AWG(a) Sizes of Solid Round Wires Used as Electrical Conductors at 20°C.

a. Values derived from ASTM B258-18.

b. A mil is equal to 1/1000 inch.

c. A circular mil is the area of a circle one mil in diameter.

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