AWG to mm Converter - gauge, area, ampacity

Gauge, diameter and area

AWG is a gauge number, not a size. It maps to a wire diameter and area through a fixed geometric series; a drop of 6 gauge numbers doubles the diameter and quadruples the area.

How American Wire Gauge works

AWG, also called the Brown & Sharpe gauge after its 1857 originators, describes the diameter of solid, round, non-ferrous wire. Two things make it awkward at first. It runs backwards - a larger number is a thinner wire - and it is logarithmic rather than linear. The number originally counted how many times a wire was drawn through progressively smaller dies, so each step is a fixed ratio, not a fixed amount.

The scale is defined precisely in ASTM B258. The diameter of gauge n is d(mm) = 0.127 × 92^{(36 − n)/39}, which fixes two anchor points: 36 AWG is exactly 0.127 mm, and 4/0 is 92 times larger at 11.68 mm. Everything in the table below comes straight from that formula. Real wire then carries a manufacturing tolerance, typically 1 to 3 percent on diameter under ASTM B3.

The shortcuts worth remembering

Because every step is the same ratio (about 1.123 in diameter), a few round numbers fall out that are worth keeping in your head:

Every 3 gauges roughly halves or doubles the cross-sectional area.
Every 6 gauges roughly halves or doubles the diameter, so it quarters or quadruples the area.
Every 10 gauges changes resistance by about 10 times - a 10 AWG wire has roughly a tenth the resistance per metre of a 20 AWG wire.

So if you know 10 AWG is about 5.26 mm², you also know 13 AWG is near 2.6 mm² and 16 AWG near 1.3 mm² without touching the formula.

AWG reference table

Solid copper conductor, computed from the ASTM B258 definition. Resistance is for copper at 20 °C; values at operating temperature are higher.

Above 4/0 the gauge scale ends; larger conductors use kcmil. 4/0 = 211.6 kcmil; the next size is 250 kcmil.
AWG	Dia (mm)	Dia (in)	Area (mm²)	Area (kcmil)	Cu Ω/km
4/0	11.684	0.4600	107.219	211.60	0.161
2/0	9.266	0.3648	67.431	133.08	0.256
1/0	8.251	0.3249	53.475	105.53	0.322
1	7.348	0.2893	42.408	83.69	0.407
2	6.544	0.2576	33.631	66.37	0.513
4	5.189	0.2043	21.151	41.74	0.815
6	4.115	0.1620	13.302	26.25	1.296
8	3.264	0.1285	8.366	16.51	2.061
10	2.588	0.1019	5.261	10.38	3.277
12	2.053	0.0808	3.309	6.53	5.210
14	1.628	0.0641	2.081	4.11	8.285
16	1.291	0.0508	1.309	2.58	13.17
18	1.024	0.0403	0.8230	1.62	20.95
20	0.8118	0.0320	0.5176	1.02	33.31
22	0.6438	0.0253	0.3255	0.64	52.96
24	0.5106	0.0201	0.2047	0.40	84.21
26	0.4049	0.0159	0.1288	0.25	133.90
28	0.3211	0.0126	0.0810	0.16	212.90
30	0.2546	0.0100	0.0509	0.10	338.53
32	0.2019	0.0080	0.0320	0.06	538.28
34	0.1601	0.0063	0.0201	0.04	855.91
36	0.1270	0.0050	0.0127	0.03	1,360.94
40	0.0799	0.0031	0.0050	0.01	3,440.87

Current-carrying capacity (ampacity)

Approximate current-carrying capacity for copper conductors from NEC Table 310.16, by insulation temperature rating. These figures assume no more than three current-carrying conductors in a raceway or cable at a 30 °C ambient, and must be derated for higher ambient or more conductors.

AWG	60 °C (A)	75 °C (A)	90 °C (A)
14	15	20	25
12	20	25	30
10	30	35	40
8	40	50	55
6	55	65	75
4	70	85	95
3	85	100	110
2	95	115	130
1	110	130	145
1/0	125	150	170
2/0	145	175	195
3/0	165	200	225
4/0	195	230	260

Ampacity is not a property of the wire alone. The 14, 12 and 10 AWG figures are further limited by NEC 240.4(D) to 15, 20 and 30 A for overcurrent protection, and all values change with ambient temperature, conductor grouping and insulation. These are for building wiring, not PCB traces - size those with the trace width calculator.

AWG, SWG and BWG are not the same

Three gauge systems share the same numbers but mean different sizes, so a bare number is ambiguous. American Wire Gauge (AWG) is the electrical standard in North America. Standard Wire Gauge (SWG, the old British imperial scale) and Birmingham Wire Gauge (BWG, used for tubing and some steel wire) are different scales with no simple formula between them. At gauge 14, for instance, AWG is 1.63 mm, SWG is 2.03 mm and BWG is 2.11 mm. If a source does not say which system it means, convert each to millimetres and compare diameters directly. Modern international practice (IEC 60228) drops gauge numbers altogether and specifies conductors by their mm² area, which removes the ambiguity.

Where engineers use this

International cable sourcing

Converting a US AWG spec to the nearest IEC 60228 metric size so a global supplier quotes a cable that actually fits the requirement.

Solar, battery and marine DC

Sizing low-voltage, high-current runs where ampacity and voltage drop, not just the gauge number, set the conductor.

Automotive and harness work

Matching gauge to current with derating for bundled conductors and high ambient temperatures in a harness.

Frequently asked questions

How do I convert AWG to mm²?

Find the diameter from the gauge with d(mm) = 0.127 × 92^((36 − n)/39), then take the area as π/4 × d². For example, 12 AWG works out to 2.053 mm diameter and 3.31 mm².

Is 12 AWG the same as 4 mm²?

Close, but not equal. 12 AWG is 3.31 mm², while 4 mm² sits nearer 11 AWG. When you substitute a metric cable for an AWG specification, round up to the next standard mm² size so you never undersize the conductor.

Does a lower AWG number mean a bigger wire?

Yes. The scale is inverse: the largest common conductor, 4/0 (also written 0000), has the lowest number, and the wire gets thinner as the number climbs. 36 AWG is just 0.127 mm.

Can I use these diameters for stranded wire?

The formula describes a solid round conductor. A stranded conductor of the same gauge carries the same copper area but has a larger overall diameter, roughly 13 to 14 percent more, because of the gaps between strands. Insulation adds more still, so never use the bare diameter for conduit fill.

What happens above 4/0?

The gauge scale ends at 4/0. Larger conductors are specified in kcmil, thousands of circular mils, which measures area directly. 4/0 equals 211,600 circular mils, and the next standard size is 250 kcmil.

How this relates to other standards

Standard / tool	Relationship	What it means
IEC 60228	Often confused with	The metric (mm2) wire-size standard; AWG is gauge-based, IEC 60228 is defined directly by area.
NEC 310.16	Ampacity from	Current ratings come from the NEC, not ASTM B258, which gives nominal dimensions only.
PCB Trace Width / Resistance	Related cross-section	Wire and trace both size by cross-sectional area and the same rho*L/A resistance physics.

Related tools and standards

Converters PCB trace width calculator Standards reference Capacitor code calculator mAh to Wh calculator PCB via current calculator Trace resistance calculator

Sources: ASTM B258-18, Standard Nominal Diameters and Cross-Sectional Areas of AWG Sizes of Solid Round Wires (dimensions) · NEC Table 310.16 (NFPA 70) for ampacity - ampacity is not defined by ASTM B258. Verify against the current edition.