Wire Gauge AWG Calculator
This calculator converts an AWG (American Wire Gauge) number to conductor diameter in millimetres, cross-sectional area in square millimetres, resistance per metre in milliohms, and an indicative maximum current capacity. AWG is the standard wire sizing system used in electronics and automotive wiring, and it is also common in New Zealand for speaker cable, marine wiring and low-voltage DC systems. The scale runs backwards: a smaller AWG number means a larger, thicker wire with lower resistance and higher current capacity. The diameter formula is d = 0.127 x 92 to the power of (36 minus AWG) divided by 39, in millimetres. From the diameter the cross-sectional area is pi divided by 4 times the diameter squared. The resistance per metre of copper at 20 degrees Celsius is rho / A, where rho = 1.724 x 10 to the minus 8 ohm-metres and A is the area in square metres. Current capacity is a general guide based on single-core copper wire in free air and should not be used for fixed building wiring design without consulting AS/NZS 3008 and a licensed electrician. In NZ building wiring, the relevant standard is AS/NZS 3000:2018 (the Wiring Rules) and cable sizing is determined by load current, installation method, grouping and ambient temperature. The calculator also accepts a custom diameter in millimetres if you know your wire size in metric terms, which is more common in European and NZ cable specifications where wire is rated by cross-sectional area (for example 1.5 mm squared or 2.5 mm squared).
Resistance at 20 C for annealed copper. Current capacity is a general guide for free-air single-core copper wire. NZ fixed wiring must be sized to AS/NZS 3008 by a licensed electrician.
How it works
The AWG diameter formula is d = 0.127 x 92^((36-AWG)/39) mm. For AWG 0 (also written 1/0), use AWG = 0; for AWG 00 use AWG = -1; for AWG 000 use AWG = -2. Cross-sectional area is A = pi/4 x d squared in mm squared. Resistance per metre is R/m = rho / A = 1.724 x 10^-8 / (A x 10^-6) in ohms per metre, displayed as milliohms per metre. Indicative current capacity is a rough guide only, taken from common free-air reference tables for single-core copper (very roughly 10 to 15 A per mm squared of cross-section for short runs in free air). Ratings for wire enclosed in conduit, grouped in a multi-core cable, or run over long distances are substantially lower.
Worked example
AWG 12: diameter = 0.127 x 92^((36-12)/39) = 0.127 x 92^(0.6154) = 0.127 x 16.17 = 2.053 mm. Cross-sectional area = pi/4 x 2.053 squared = 3.309 mm squared. Resistance per metre = 1.724 x 10^-8 / (3.309 x 10^-6) = 5.21 milliohms per metre. The indicative maximum current for AWG 12 as a single core in free air is approximately 41 A. These match the default values above. Note that this free-air figure is much higher than the rating for the same conductor enclosed in conduit or grouped in a multi-core cable, which for AWG 12 in NZ building wiring is typically around 20 A; fixed wiring must be sized to AS/NZS 3008 by a licensed electrician.
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