AWG to mm² converter
Convert any American Wire Gauge size to square millimetres — and back again — based on the conductor's true cross-sectional area, with the nearest standard metric size shown alongside.
AWG (ASTM B258) and mm² (IEC 60228) are different standards, so most sizes don't match exactly. The nearest standard size is shown with whether it rounds up or down — direction matters when sizing for current.
Why AWG and mm² don't line up
AWG and mm² come from two different worlds. AWG is a geometric scale defined by ASTM B258: diameters step by a fixed ratio, so the numbers are logarithmic. Metric conductors follow IEC 60228, which specifies a separate list of standard cross-sections — 1.5, 2.5, 4, 6, 10 mm² and so on — chosen for manufacturing, not to mirror AWG. Because the two scales were never designed to match, almost no AWG size equals a round metric size exactly.
That is why a fixed "AWG = mm²" lookup table is misleading. The honest way to convert is to compute the conductor's actual area from its gauge, then report the nearest standard metric size — noting whether it rounds up or down. Rounding the wrong way can leave a circuit undersized, so the direction of the nearest match matters.
The math behind it
Every AWG diameter comes from one formula. For a gauge number n, the diameter in inches is:
d(in) = 0.005 × 92(36 − n) / 39
The aught sizes extend the scale below 1 AWG: 1/0 uses n = 0, 2/0 uses −1, 3/0 uses −2, and 4/0 uses −3. Convert that diameter to millimetres, and the cross-sectional area in mm² is simply π × (d / 2)². The converter does this exactly, then matches the result to the closest IEC 60228 size — which is the number you actually order cable by outside North America.
Sizing for current, not just diameter? The metric equivalent of a gauge does not by itself tell you the safe load — see ampacity & wire size for the NEC current ratings and their limits.