AWG to mm² Calculator

AWG to mm² Calculator results give the exact copper area of a wire gauge in mm², the next IEC metric cable size up, and the resistance, diameter and weight of the conductor itself.

AWG to mm² Calculator for Wire and Cable

American wire is sold by gauge and kcmil, while most of the world sells cable by its area in square millimeters. The two series were built differently, so a US gauge almost never lands on a metric size.

Electricians use the conversion when imported equipment, a solar kit or an RV calls for metric cable, and engineers use it to check a European spec against US wire. Hobbyists use it the other way, to find which AWG matches the mm² printed on a battery lead or speaker cable.

The AWG to mm² Calculator works in both directions. It gives the exact area, the metric sizes on either side, the solid and stranded diameter, the DC resistance at any temperature, and the bare copper or aluminum weight.

Converting AWG to mm² and mm² to AWG

In the AWG to mm² Calculator, pick a size from 1000 kcmil down to 40 AWG, then solid or stranded and copper or aluminum. For mm² to AWG, enter a metric area or pick a standard size from 0.5 to 500 mm².

The accordion sets the conductor temperature for the resistance figures. It defaults to the 20 °C reference that IEC 60228 and most wire tables use, with presets up to the 90 °C rating of common building wire insulation.

AWG to mm² Formula

AWG diameters follow ASTM B258, which fixes 4/0 at 0.4600 inch and 36 AWG at 0.0050 inch and spaces the 38 sizes between them evenly on a ratio. In millimeters, the diameter of gauge n works out as follows.

$$d_n=0.127\times 92^{(36-n)/39}$$

The area then comes from the circle formula. Sizes 1/0 through 4/0 use n = 0, -1, -2 and -3, and kcmil sizes skip the formula, since 1 kcmil is 0.5067 mm².

$$A=\frac{\pi }{4}\times d_n^2$$

For 12 AWG, that gives a 2.053 mm diameter and 3.309 mm², or 6,530 circular mils. The same 6,530 circular mils and 3.31 mm² appear for solid 12 AWG in NEC Chapter 9 Table 8, as reproduced in this NECA-IBEW copy of Table 8.

The common mistake is reading a metric swap as an equal size. Quick lists often pair 12 AWG with 4 mm² and 10 AWG with 6 mm², but those are the next metric sizes up, while the true areas are 3.31 and 5.26 mm².

Why Metric Cable Sizes Never Match AWG

IEC 60228 does not fix an exact area for each metric size. It sets a maximum DC resistance at 20 °C, so a 4 mm² cable is any conductor that tests at 4.61 Ω/km or less, whatever its measured area.

The IEC 60228 summary from cable maker Nexans lists those class 2 stranded copper limits. Comparing them with the AWG resistance shows whether a metric swap carries as well.

The AWG column is solid annealed copper from the area, and every next IEC size has the lower resistance. That is why the alert box in the AWG to mm² Calculator can call the larger metric size an equal or better swap.

Going From mm² to AWG

The reverse direction hides a trap. Every common metric size from 1.5 to 16 mm² sits just above an even US gauge, so the closest AWG carries less copper than the metric cable.

A 2.5 mm² circuit replaced with 14 AWG loses about 17% of its area, and 4 mm² replaced with 12 AWG loses 17% as well. The 6 mm² to 10 AWG swap is 12% short, and 10 mm² to 8 AWG is 16% short.

The first card shows both the closest gauge and the smallest one with at least as much copper, such as 12 AWG for a 2.5 mm² circuit. If the run was sized tight, take the larger one and check it with the Wire Ampacity Calculator and Voltage Drop Calculator.

Stranded Diameter, Resistance and Weight

Stranded wire is larger across than solid wire of the same gauge, because of the gaps between strands. The AWG to mm² Calculator uses the ASTM B8 class B strand counts of 7, 19, 37 and 61. That gives 12 AWG stranded as 7 wires about 2.33 mm across, against 2.32 mm in NEC Table 8.

Table 8 also lists an area for stranded wire, 4.25 mm² for 12 AWG, but its notes say that figure is the circle around the strands. The copper area is still 3.31 mm², and compact stranding comes out about 9% smaller across than the standard round build.

Resistance is the resistivity over the area, corrected for temperature. Copper uses 17.241 Ω·mm²/km with a coefficient of 0.00393, and EC aluminum, at 61% of copper's conductivity, uses 28.264.

$$R_T=\frac{\rho }{A}\times (1+\alpha \times (T-20))$$

For 12 AWG copper, that is 5.211 Ω/km at 20 °C and 6.34 Ω/km at 75 °C, which is 1.93 Ω per 1,000 feet. That 75 °C figure matches NEC Table 8, and the Wire Resistance Calculator carries it over a full run length.

Real wire runs slightly under its nominal size. An electrician on the Mike Holt forum measured three brands of solid 12 AWG at 0.0785 to 0.0791 inch, against a nominal 0.0808 inch.

AWG to mm² Questions by Gauge

What is 12 AWG in sq mm?

12 AWG is 3.31 mm², with a 2.05 mm solid diameter. It is not 2.5 mm² or 4 mm², though 4 mm² is the metric size that carries at least as much, at 4.61 Ω/km against 5.21 Ω/km for 12 AWG.

Going the other way, 2.5 mm² cable is about 24% smaller than 12 AWG. It should not replace 12 AWG on a circuit sized for 12 AWG, even though the two are often listed side by side.

What is 14 AWG in sq mm?

14 AWG is 2.08 mm², with a 1.63 mm solid diameter. The next metric size up is 2.5 mm², which has 20% more area and a resistance limit of 7.41 Ω/km against 8.29 Ω/km for solid 14 AWG.

The next metric size down, 1.5 mm², has 28% less area than 14 AWG. That is too large a drop to treat as an equivalent on a power circuit, so pick 2.5 mm² when replacing 14 AWG.

What is 18 AWG in sq mm?

18 AWG is 0.823 mm², with a 1.02 mm solid diameter. Lists often pair it with 0.75 mm², which is 9% smaller, while 1 mm² is the next size up and the one the AWG to mm² Calculator suggests.

For control wiring and appliance cords, check which one the equipment maker calls for. For a direct swap that carries at least as much current with no more voltage drop, use 1 mm².

What is 4 AWG in mm²?

4 AWG is 21.15 mm², with a 5.19 mm solid diameter. Stranded 4 AWG uses 7 strands, and the next metric size up is 25 mm², at 0.727 Ω/km against 0.815 Ω/km for solid 4 AWG.

The next metric size down, 16 mm², is 24% smaller than 4 AWG. That gap is why 16 mm² battery and inverter cable is not a drop-in match for a 4 AWG run, while 25 mm² is.

What is 32 AWG in mm²?

32 AWG is 0.0320 mm², with a 0.202 mm diameter. That is far below 0.5 mm², the smallest size in IEC 60228, so metric hookup wire this fine is sold by its own area or by AWG.

The AWG to mm² Calculator flags gauges finer than about 0.4 mm² as outside the IEC range. Match such wire by area instead, and check its resistance on the maker's sheet.