Convert American Wire Gauge sizes from 4/0 to 40 AWG into diameter (mm and inches), cross-section (mm² and kcmil) and resistance per kilometre, or go the other way from a millimetre size to the nearest gauge.
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How to use the AWG to MM
Choose the direction: AWG to mm, or a mm / inch diameter or mm² area to AWG.
Pick the gauge or type the size.
Choose copper or aluminum for the resistance figures.
Read the diameter, area and resistance, with the formula steps.
Scroll the full gauge table or download it as CSV.
AWG formulas
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Formula
Example (12 AWG)
Diameter (mm)
d = 0.127 × 92^((36 − n) ÷ 39)
2.053 mm
Diameter (in)
d = 0.005 × 92^((36 − n) ÷ 39)
0.0808 in
Area (mm²)
A = π ÷ 4 × d²
3.309 mm²
Area (kcmil)
A = (d in mils)² ÷ 1000
6.53 kcmil
Gauge from diameter
n = 36 − 39 × log92(d ÷ 0.127 mm)
2.053 mm → 12
Resistance
R = ρ × L ÷ A
copper: 5.21 Ω/km
The American Wire Gauge (ASTM B258) defines 36 AWG as 0.005 in and 0000 (4/0) as 0.46 in, with 39 equal geometric steps between them. That is why the ratio between neighbouring gauges is the 39th root of 92, about 1.1229.
Common gauges at a glance
AWG
Diameter mm
Area mm²
Nearest metric size
Typical use
4/0
11.68
107.2
120 mm²
Service entrance, large battery cables
2
6.544
33.6
35 mm²
Feeders, inverter cables
6
4.115
13.3
16 mm²
Ranges, EV chargers, sub-panels
10
2.588
5.26
6 mm²
Dryers, water heaters, 30 A circuits
12
2.053
3.31
4 mm² (2.5 mm² is smaller)
20 A household circuits
14
1.628
2.08
2.5 mm²
15 A lighting circuits
18
1.024
0.823
1 mm²
Lamp cords, thermostat wire
22
0.644
0.326
0.5 mm² (0.34 mm² class)
Hook-up wire, data cables
24
0.511
0.205
0.25 mm² class
Ethernet (Cat5e/Cat6) conductors
30
0.255
0.0509
0.05 mm² class
Wire-wrap, fine electronics
For choosing a conductor by current and length, use a wire size or voltage drop calculator and your local electrical code; this page converts sizes only.
Frequently asked questions
How do I convert AWG to mm?
Use d(mm) = 0.127 × 92^((36 − n) ÷ 39), where n is the gauge number (use 0 for 1/0, −1 for 2/0, −2 for 3/0 and −3 for 4/0). For 12 AWG that gives 2.053 mm.
How do I convert AWG to mm²?
Find the diameter first, then area = π ÷ 4 × d². 12 AWG is 3.31 mm², 14 AWG is 2.08 mm² and 10 AWG is 5.26 mm².
What AWG is 2.5 mm² wire?
2.5 mm² sits between 14 AWG (2.08 mm²) and 12 AWG (3.31 mm²); its exact equivalent is about 13.2 AWG. When current capacity matters, round to the thicker gauge, 12 AWG.
Why do bigger AWG numbers mean thinner wire?
The gauge number originally counted how many drawing dies the wire passed through. More draws made thinner wire, so 40 AWG is very fine and 4/0 (0000) is thick.
How does the size change from one gauge to the next?
Each gauge step changes the diameter by a factor of about 1.1229. Six gauges halve or double the diameter, and three gauges halve or double the cross-section area and roughly double or halve the resistance.
Is the table for solid or stranded wire?
The diameters are for a solid round conductor. Stranded wire of the same gauge has about the same copper area but a slightly larger overall diameter because of the gaps between strands.
What resistivity is used?
Annealed copper at 20 °C, 0.017241 Ω·mm²/m (the IACS standard), and aluminum at 0.0282 Ω·mm²/m. Resistance rises with temperature by about 0.39% per °C for copper.
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