Wire Gauge Converter
American Wire Gauge runs backwards: a higher number means thinner wire. Diameter in millimetres is 0.127 multiplied by 92 to the power of 36 minus the gauge, divided by 39. Every six gauges roughly halves the diameter, and every three halves the area.
- AWG gauge12
- Diameter2.053 mm
- Diameter in inches0.0808 in
- Cross-sectional area3.309 mm²
- Resistance, solid copper0.01 Ω/km
| AWG | Diameter | Area | Copper |
|---|---|---|---|
| 1/0 | 8.25 mm | 53.48 mm² | 0.00 Ω/km |
| 2 | 6.54 mm | 33.63 mm² | 0.00 Ω/km |
| 4 | 5.19 mm | 21.15 mm² | 0.00 Ω/km |
| 6 | 4.12 mm | 13.30 mm² | 0.00 Ω/km |
| 8 | 3.26 mm | 8.37 mm² | 0.00 Ω/km |
| 10 | 2.59 mm | 5.26 mm² | 0.00 Ω/km |
| 12 | 2.05 mm | 3.31 mm² | 0.01 Ω/km |
| 14 | 1.63 mm | 2.08 mm² | 0.01 Ω/km |
| 16 | 1.29 mm | 1.31 mm² | 0.01 Ω/km |
| 18 | 1.02 mm | 0.82 mm² | 0.02 Ω/km |
| 20 | 0.81 mm | 0.52 mm² | 0.03 Ω/km |
| 22 | 0.64 mm | 0.33 mm² | 0.05 Ω/km |
| 24 | 0.51 mm | 0.20 mm² | 0.08 Ω/km |
How to convert AWG to millimetres
Choose what you know
Pick whether you have a gauge number, a measured diameter in millimetres, or a cross-sectional area in square millimetres.
Enter the value
Type it in. Diameters and areas that fall between gauges report the nearest standard gauge.
Read the conductor
Diameter, area in square millimetres, diameter in inches, and resistance per kilometre of solid copper all appear at once.
Check the chart
Compare against the common gauges table for the sizes either side of yours.
Why use this tool
Works in three directions
Start from a gauge, a measured diameter, or the square-millimetre rating on a European cable and get the other two.
The real formula, not a lookup
Diameter is computed from the AWG definition, so fractional and out-of-chart gauges still resolve correctly.
Resistance included
Ohms per kilometre for solid copper at 20°C, which is usually the number you actually wanted the area for.
Handles 4/0 through 40
The heavy gauges written 4/0 to 1/0 are covered as well as the thin end of the scale.
Runs entirely in your browser
Nothing you type is uploaded or stored.
About this tool
American Wire Gauge is the standard for conductor sizes in North America, and it confuses people for two reasons. The numbering runs backwards, so 10 AWG is thicker than 20 AWG, and the heaviest sizes are written as 1/0 through 4/0 rather than as zero and negative numbers. The scale exists because wire is made by drawing it through progressively smaller dies, and the gauge number originally counted how many drawing steps it had been through.
That history is why AWG is logarithmic rather than linear. Diameter in millimetres works out to 0.127 multiplied by 92 raised to the power of 36 minus the gauge, all divided by 39. Two useful shortcuts fall out of it: every six gauges roughly halves the diameter, and every three gauges roughly halves the cross-sectional area. This tool computes the formula rather than reading a table, so it stays accurate between the whole numbers and at the ends of the scale.
Most of the time the reason you want a gauge is the area, and the reason you want the area is resistance. A conductor resistance is its resistivity times length divided by area, so the square-millimetre figure is what feeds a voltage-drop calculation. The resistance shown here is for solid copper at 20°C; stranded wire is slightly higher for the same nominal area, aluminium is around 60 percent more resistive, and resistance rises with temperature. Outside North America cable is specified directly in square millimetres, which is why the area column matters when matching a European part to an AWG one. For the surrounding arithmetic there is the unit converter, the length converter, and the metric prefix converter.
Frequently asked questions
- What is 12 AWG in millimetres?
- 12 AWG is 2.053 millimetres in diameter, which is a cross-sectional area of 3.31 square millimetres. That is the usual size for a 20 amp circuit in North American house wiring.
- Why do higher AWG numbers mean thinner wire?
- Because the number originally counted how many times the wire had been drawn through a die to reach its size. More draws meant more reduction, so a higher number is a thinner conductor.
- What does 4/0 mean?
- It is the notation for gauges above zero, read as "four aught". The sequence going up in size is 1, 0, 1/0, 2/0, 3/0, 4/0, with 4/0 being the heaviest standard AWG conductor at about 11.7 millimetres.
- How do I match an AWG size to a European cable?
- Compare cross-sectional area in square millimetres rather than gauge numbers, since that is how cable is specified outside North America. 12 AWG is 3.31 mm², which sits between the common 2.5 mm² and 4 mm² sizes.
- Is the resistance figure accurate for stranded wire?
- It is a good approximation but slightly low. Stranded conductors have marginally more resistance than solid wire of the same nominal area, and resistance also rises with temperature.
- Is my data uploaded anywhere?
- No. The calculation runs in your browser and nothing you type leaves your device.
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