Wire gauge converter

How many mm² is that AWG wire?

Convert AWG to mm², kcmil and diameter, with the copper resistance per kilometre.

Wire size

From

Result

13.21 AWG

2.5 square millimetres is about 13.21 AWG

Nearest whole gauge at least this thick: 13 AWG
Solid copper of this size: 6.9 Ω per km at 20 °C

In all units

Square millimetres: 2.5 mm²
American Wire Gauge: 13.21 AWG
Thousand circular mils: 4.934 kcmil
Diameter in millimetres: 1.784 mm Ø
Diameter in inches: 0.07024 in Ø

AWG sizes

American Wire Gauge sizes from 4/0 to 30 with the diameter in millimetres, the cross-section and the resistance of copper wire.

AWG sizes
AWG	Diameter, mm	Cross-section, mm²	Copper, Ω/km
4/0	11.68	107.2	0.161
3/0	10.4	85.03	0.203
2/0	9.266	67.43	0.256
1/0	8.251	53.48	0.322
1	7.348	42.41	0.407
2	6.544	33.63	0.513
3	5.827	26.67	0.646
4	5.189	21.15	0.815
5	4.621	16.77	1.03
6	4.115	13.3	1.3
7	3.665	10.55	1.63
8	3.264	8.366	2.06
9	2.906	6.634	2.6
10	2.588	5.261	3.28
11	2.305	4.172	4.13
12	2.053	3.309	5.21
13	1.828	2.624	6.57
14	1.628	2.081	8.29
15	1.45	1.65	10.4
16	1.291	1.309	13.2
17	1.15	1.038	16.6
18	1.024	0.823	20.9
19	0.9116	0.6527	26.4
20	0.8118	0.5176	33.3
21	0.7229	0.4105	42

Convert AWG to mm², kcmil and diameter, with the copper resistance per kilometre.

How to use

Type the wire size and choose its unit: mm², AWG, kcmil or the diameter.
Pick the unit to convert to. For the gauges 1/0 to 4/0, type 0 to −3.
Read the size in every unit, the nearest whole gauge and the copper resistance. The table lists the common gauges.

How it works

Europe sells wire by its cross-section in square millimetres, North America by its American Wire Gauge number. The gauge counts backwards: a bigger number is a thinner wire, because it once counted how many times the wire was drawn through a die. Every 6 gauges halve the diameter, and every 3 gauges halve the cross-section.

The ASTM B258 standard defines the diameter of gauge n as d = 0.127 mm × 92^((36 − n) / 39), from 0.127 mm at 36 AWG to 11.684 mm at 4/0. The cross-section is A = π d² / 4: 12 AWG is 2.053 mm across and 3.31 mm², so a 2.5 mm² house wire falls between 14 and 13 AWG. Copper's resistance follows R = ρ L / A with ρ = 1/58 Ω·mm²/m at 20 °C, so 1 km of 2.5 mm² copper is 6.9 Ω.

The formula is for solid round wire. Stranded wire of the same gauge has the same copper but is slightly wider. How much current a wire may carry depends on insulation, installation and local rules, so it is not shown here.

Frequently asked questions

What AWG is 2.5 mm²?

About 13.2 AWG. 13 AWG (2.63 mm²) is the nearest gauge at least as thick, and 14 AWG (2.08 mm²) is thinner.

What do 1/0, 2/0 and 4/0 mean?

They are the gauges thicker than 0, also written 0, 00 and 0000. In the calculator they are 0, −1 and −3.

Can I use this to choose a cable for a circuit?

Only as a size conversion. The allowed current depends on the insulation, the installation method and the electrical code where you live.

Does the diameter include the insulation?

No. It is the diameter of a bare solid round conductor. Do not use the outside diameter of an insulated cable as the input.

Can I use the resistance value for aluminium wire?

No. The resistance shown is for annealed copper at 20 °C. Other materials and temperatures give different resistance, even at the same cross-section.

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