What is 12 AWG in mm²?

3.31 mm², with a conductor diameter of 2.053 mm. The nearest metric cable size sold in Europe is 2.5 mm², which is slightly smaller, or 4 mm² if you need to be sure of matching it.

How many amps can 12 gauge wire carry?

20 A at a 60 °C insulation rating, 25 A at 75 °C and 30 A at 90 °C in the NEC table, before derating. Circuit protection is usually sized to the 60 °C column for general branch circuits.

Why do AWG numbers get smaller as the wire gets thicker?

The number counts drawing operations. Wire is pulled through successively smaller dies, so a higher number means more passes and a thinner conductor — and the very thick sizes ran out of numbers, which is why they are written 0, 00, 000 and 0000.

How much does wire resistance change with temperature?

Copper rises about 0.39 per cent per degree Celsius. A conductor running at 75 °C has roughly 22 per cent more resistance than the same wire at 20, which matters on a long run near its voltage drop limit.

What is kcmil and where is it used?

Thousands of circular mils, an area unit where one circular mil is the area of a circle a thousandth of an inch across. North American codes use it for conductors larger than 4/0, where AWG numbering stops.

Wire Gauge Converter

Convert AWG to square millimetres, diameter, resistance and an ampacity figure, for copper or aluminium.

The Wire Gauge Converter runs entirely in your browser. The tables ship with the page and your inputs stay on your device.

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About Wire Gauge Converter

American Wire Gauge is a geometric series rather than a table someone wrote down: each step down in gauge multiplies the diameter by the 39th root of 92, which is why every three gauges roughly doubles the cross-sectional area and every six halves the diameter. That formula is what this converter runs, in both directions, so an AWG number becomes a diameter, a cross-section in square millimetres and kcmil, and a metric cable size finds its closest gauge. Resistance follows from the same geometry, corrected for conductor temperature and for aluminium. Ampacity is the one figure that is not geometry — it comes from the NEC table, and is shown as guidance rather than as a substitute for your local code.

Features

AWG to mm², diameter in mm and inches, and kcmil, from 4/0 to 40
Metric cross-section back to the nearest AWG gauge
DC resistance per kilometre and per 1,000 feet, for copper or aluminium
Resistance corrected for conductor temperature
Conductor mass per kilometre, for shipping and pull calculations
NEC 310.16 ampacity at 60, 75 and 90 °C insulation ratings
Resistance of a run of the length you enter
Full reference table with the selected gauge highlighted

How to use the Wire Gauge Converter

Pick a direction: AWG to metric, or metric to AWG
Choose the gauge or type the cross-section
Set the conductor material and the insulation temperature rating
Read the dimensions, resistance and ampacity, and add a run length for its total resistance

Example

Input

12 AWG copper

Output

2.053 mm diameter · 3.31 mm² · 5.21 Ω/km · 25 A at 75 °C

The metric equivalent sold in Europe would be 2.5 mm², slightly smaller than 12 AWG.

Common errors & troubleshooting

The metric match is not an exact figure. — It cannot be. AWG and metric cable sizes come from different series, so 2.5 mm² sits between 13 and 14 AWG — the tool reports the closest standard gauge and the real area.
The resistance does not match the NEC table. — NEC Chapter 9 Table 8 is quoted at 75 °C, and this defaults to 20 °C. Set the conductor temperature to 75 and the figures line up.
There is no ampacity for a thin gauge. — The NEC table starts at 14 AWG for building wiring. Thinner conductors are covered by other standards for chassis wiring and electronics, where the limits depend heavily on bundling and airflow.
Aluminium seems to need a much larger conductor. — It does. Aluminium's resistivity is about 60 per cent higher than copper's, so it is usually sized two gauges larger for the same current.

Frequently asked questions

What is 12 AWG in mm²?: 3.31 mm², with a conductor diameter of 2.053 mm. The nearest metric cable size sold in Europe is 2.5 mm², which is slightly smaller, or 4 mm² if you need to be sure of matching it.
How many amps can 12 gauge wire carry?: 20 A at a 60 °C insulation rating, 25 A at 75 °C and 30 A at 90 °C in the NEC table, before derating. Circuit protection is usually sized to the 60 °C column for general branch circuits.
Why do AWG numbers get smaller as the wire gets thicker?: The number counts drawing operations. Wire is pulled through successively smaller dies, so a higher number means more passes and a thinner conductor — and the very thick sizes ran out of numbers, which is why they are written 0, 00, 000 and 0000.
How much does wire resistance change with temperature?: Copper rises about 0.39 per cent per degree Celsius. A conductor running at 75 °C has roughly 22 per cent more resistance than the same wire at 20, which matters on a long run near its voltage drop limit.
What is kcmil and where is it used?: Thousands of circular mils, an area unit where one circular mil is the area of a circle a thousandth of an inch across. North American codes use it for conductors larger than 4/0, where AWG numbering stops.

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