How is AWG diameter calculated?

AWG uses an exact geometric formula: diameter in millimetres equals 0.127 times 92 raised to the power (36 minus the gauge number) divided by 39. Each step of six gauges roughly halves the diameter, and ten gauges divides the area by about ten.

What do 4/0 and 0000 mean?

Gauges thicker than 1 are written with multiple zeros: 1/0 (one ought), 2/0, 3/0, and 4/0 (four ought, also written 0000). In the formula they correspond to gauge numbers 0, minus 1, minus 2, and minus 3, getting progressively larger in diameter.

Why are two ampacity figures shown?

Chassis wiring assumes a single insulated conductor in free air where heat dissipates easily, allowing higher current. Power transmission assumes conductors bundled or in conduit, where heat builds up, so the safe current is much lower. Real installations use the more conservative figure.

Does a higher AWG number mean thicker or thinner wire?

Thinner. AWG is inverse: the larger the gauge number, the smaller the wire. A 40 AWG wire is hair-thin, while 0000 (4/0) is roughly half an inch across. This is the opposite of how most people first expect it to work.

Can I rely on this for wiring a circuit?

Use it as a reference for diameter and area, but always size conductors for a real circuit using your national electrical code (such as the NEC) accounting for insulation rating, ambient temperature, conductor material, and installation method. The ampacity values here are general engineering references, not code values.

AWG Wire Gauge Reference Table

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American Wire Gauge (AWG) is the standard system for the diameter of round, solid, nonferrous electrical wire in North America. This reference computes the exact diameter, cross-sectional area, and a reference ampacity for every gauge from 0000 (4/0) down to 40.

How it works

AWG is defined by a precise geometric progression rather than a lookup table. The bare conductor diameter follows:

d(mm) = 0.127 × 92^((36 − n) / 39)

where n is the gauge number. The four oversized gauges 1/0, 2/0, 3/0, and 4/0 correspond to n values of 0, −1, −2, and −3. From the diameter, the cross-sectional area is π/4 × d². Two consequences fall out of the formula: each 6-gauge step roughly halves the diameter, and each 10-gauge step divides the area by about ten.

The table also lists a reference ampacity in two columns. Chassis wiring (a single conductor in free air) tolerates more current than power transmission (bundled or in conduit) because heat escapes more easily.

Example and notes

Note the inverse scale: a larger gauge number means a thinner wire. Common 12 AWG house wiring is about 2.05 mm in diameter with a 3.3 mm² cross-section, while 0000 (4/0) is roughly 11.7 mm across — used for service entrances and large feeders. These ampacity numbers are general engineering references; for any real circuit, size conductors using your national electrical code, which factors in insulation temperature rating, ambient conditions, conductor material, and how the wire is installed.