Converter

Wire Gauge Converter

Convert between AWG, mm², mm diameter, and circular mils. Full reference table from 0000 to 40 AWG with resistance values.

Quick Answer

AWG 12 = 3.31 mm² = 2.053 mm diameter = 6,530 circular mils. Common for 20A household circuits. Use our converter for any gauge lookup.

AWG
12
mm²
3.3090
Diameter (mm)
2.0530
Circular Mils
6,530
Resistance (Ω/km)
5.2110

Showing closest match for AWG 12

About This Tool

The Wire Gauge Converter is a precision reference tool for electricians, engineers, hobbyists, and anyone working with electrical wire. It provides instant bidirectional conversion between the four most commonly used wire measurement systems: American Wire Gauge (AWG), cross-sectional area in square millimeters (mm²), diameter in millimeters, and circular mils. Each lookup also returns the copper resistance per kilometer, making it invaluable for voltage drop calculations and circuit design.

Understanding American Wire Gauge (AWG)

The American Wire Gauge system, also known as the Brown & Sharpe gauge, has been the standard wire sizing system in North America since 1857. The system is counter-intuitive at first glance because larger gauge numbers indicate thinner wire. This originated from the manufacturing process: wire was drawn through progressively smaller dies, and the gauge number represented the number of drawing operations. AWG 0000 (often written as 4/0) is the largest standard size at 11.684 mm diameter, while AWG 40 is hair-thin at just 0.08 mm. The scale is logarithmic, meaning each step follows a geometric progression. Specifically, each increase of 6 AWG numbers halves the cross-sectional area, and each increase of 3 numbers doubles the resistance per unit length.

Metric Wire Sizes (mm² and mm diameter)

Most of the world outside North America uses metric wire sizing, specifying wire by its cross-sectional area in square millimeters. The IEC 60228 standard defines preferred metric wire sizes: 0.5, 0.75, 1.0, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240, 300, 400, 500, 630, 800, and 1000 mm². These do not correspond exactly to AWG sizes, which can cause confusion when working with international specifications. For example, AWG 14 is 2.08 mm², which falls between the standard metric sizes of 1.5 mm² and 2.5 mm². Our converter helps bridge this gap by finding the closest AWG equivalent to any metric size and vice versa.

Circular Mils Explained

Circular mils (cmil or MCM) are a uniquely American unit of area designed specifically for round conductors. One circular mil is the area of a circle with a diameter of one mil (0.001 inch). The advantage of circular mils is computational simplicity: the area in circular mils equals the diameter in mils squared, without needing pi. For larger conductors, the unit kcmil (thousands of circular mils, formerly MCM) is used. For instance, a 500 kcmil cable has an area of 500,000 circular mils. The NEC (National Electrical Code) uses circular mils extensively in its ampacity tables, making this unit essential for electrical code compliance work.

Resistance and Voltage Drop

Wire resistance is critical for electrical system design. Higher resistance means more energy lost as heat and greater voltage drop over distance. Our tool displays resistance in ohms per kilometer for copper conductors at 20 degrees Celsius. To calculate voltage drop, multiply the resistance per unit length by the current and the total wire length (round trip, so double the one-way distance). The NEC recommends that voltage drop not exceed 3% on branch circuits and 5% total for the combination of feeder and branch circuit. For a 120V, 20A circuit on 12 AWG wire (5.211 ohms/km), the maximum one-way run before exceeding 3% drop is approximately 17 meters (56 feet).

Common Applications by Wire Gauge

Different wire gauges serve different purposes. AWG 0000 to 2 are used for main electrical service entrance cables and large motor feeders. AWG 4-6 handle electric ranges, central air conditioning, and sub-panels. AWG 8-10 are common for dryer circuits, water heaters, and 30-amp circuits. AWG 12 is the workhorse of residential wiring for 20-amp general-purpose circuits. AWG 14 serves 15-amp lighting circuits. AWG 16-18 handle extension cords, lamp cords, and low-power appliances. AWG 20-24 are used for thermostat wire, doorbells, and data cables (Cat5e uses 24 AWG solid conductors). AWG 26 and smaller are found in electronics, telecommunications, and fine instrumentation. Understanding which gauge fits your application is essential for safety and code compliance.

Frequently Asked Questions

What is AWG and how does it work?
AWG stands for American Wire Gauge, a standardized system used in North America to denote the diameter of electrically conducting wire. The gauge number is inversely related to diameter: a smaller AWG number means a thicker wire. AWG 0000 (4/0) is the thickest standard gauge at 11.684 mm diameter, while AWG 40 is extremely thin at 0.0799 mm. Each step of 6 AWG numbers doubles the wire cross-sectional area, and each step of 3 AWG numbers doubles the resistance. The system originated from the number of times wire was drawn through progressively smaller dies during manufacturing.
How do I convert AWG to mm²?
AWG to mm² conversion does not follow a simple linear formula because the AWG scale is logarithmic. The formula is: diameter (mm) = 0.127 x 92^((36-AWG)/39), and area (mm²) = pi/4 x diameter². For common conversions: AWG 10 = 5.26 mm², AWG 12 = 3.31 mm², AWG 14 = 2.08 mm², AWG 16 = 1.31 mm². Our tool uses precise reference values from ASTM B258 standards for maximum accuracy rather than calculated approximations.
What wire gauge do I need for my project?
The required wire gauge depends on current capacity (ampacity), voltage drop, and run length. For residential wiring in the US: 15-amp circuits use 14 AWG, 20-amp circuits use 12 AWG, and 30-amp circuits use 10 AWG. For automotive applications, 16-18 AWG handles most accessories, while starter cables need 4-6 AWG. For speaker wire, 16 AWG works for runs under 50 feet; use 12-14 AWG for longer distances. Always consult the National Electrical Code (NEC) or a licensed electrician for permanent installations.
What are circular mils and why are they used?
A circular mil (cmil) is a unit of area equal to the area of a circle with a diameter of one mil (0.001 inch). It simplifies calculations for round conductors because you simply square the diameter in mils rather than using pi. For example, a wire with a 100-mil diameter has an area of 10,000 circular mils. This unit is widely used in the American electrical industry and in NEC tables for conductor sizing. One circular mil equals approximately 0.0005067 mm² or 0.7854 square mils.
What is the difference between AWG and SWG?
AWG (American Wire Gauge) and SWG (Standard Wire Gauge, also called Imperial Wire Gauge) are two different systems. SWG is used primarily in the UK and some Commonwealth countries, while AWG is the North American standard. The two systems assign different diameters to the same gauge numbers. For example, SWG 10 has a diameter of 3.251 mm, while AWG 10 has a diameter of 2.588 mm. SWG also covers a wider range (0000000 to 50) compared to AWG (0000 to 40). When ordering wire internationally, always confirm which gauge system is being referenced.
How does wire gauge affect resistance and voltage drop?
Thinner wire (higher AWG number) has greater resistance per unit length, which causes more voltage drop over distance. The relationship is logarithmic: every 3 AWG steps doubles the resistance. For example, AWG 14 has about 8.29 ohms/km while AWG 11 has about 4.13 ohms/km. Excessive voltage drop can cause equipment malfunction, dimming lights, or overheating. The NEC recommends keeping voltage drop below 3% for branch circuits and 5% total for feeder plus branch circuits. Use our resistance values to calculate voltage drop: V_drop = Current x Resistance x Length x 2 (for round trip).

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