How to use it
- Type an AWG number in the box, such as 12, or a cross-section such as 2.5 mm².
- Read Wire gauge and Diameter: the diameter is given in millimetres and in mil.
- Read Cross-section and Nearest IEC 60228 size to choose a standard conductor size in your country.
- Open AWG table, 0000 to 40 to compare the sizes side by side.
How the diameter is calculated
The American Wire Gauge numbers are set by a geometric series: each step down in number makes the wire about 12 % thicker. The ASTM B258 standard gives the diameter with a formula, and the table below follows from it.
d = 0.005 in × 92^((36 − n) ÷ 39)
n gauge number, from 36 down to 0
0000 is n = −3, 000 is n = −2, 00 is n = −1
Area = π ÷ 4 × d² d in millimetres (1 in = 25.4 mm)- The formula and the table of diameters are from Wikipedia, American wire gauge, which cites ASTM B258.
- A conductor's area is the nominal area of the wire. Stranded conductors and insulation change the overall size.
Metric sizes and what they mean
Metric conductors are sold by their cross-section in mm², in the sizes of IEC 60228: 0.5, 0.75, 1, 1.5, 2.5, 4, 6, 10, 16, 25 mm² and so on. The nearest size shown is the closest one by area, not a rule for which size to buy.
What this table does not cover
- Current ratings for each size, which depend on the insulation, the installation and the local rules.
- Stranded or flexible conductors with the same area, and the resistance per metre of each size.
Worked example: AWG 12
AWG 12 has n = 12, so d = 0.005 in × 92^(24 ÷ 39) = 0.08081 in = 80.81 mil, which is 2.053 mm.
Its area is π ÷ 4 × (2.053 mm)² = 3.309 mm². The nearest IEC 60228 size is 4 mm².
Frequently asked questions
Why is a bigger AWG number a thinner wire?
AWG counts down: the number is a step in a geometric series, so AWG 10 is thicker than AWG 12, which is thicker than AWG 14. The 0000 wire is the thickest of the table.
What does 0000 mean?
It is the largest size in the common gauge, read as four zeros, and it has a diameter of 0.46 in (about 11.7 mm). 000 and 00 are the sizes between it and AWG 0.
Is AWG 12 the same as 4 mm²?
No. AWG 12 has an area of 3.309 mm², which is between the IEC sizes 2.5 mm² and 4 mm²; the nearest standard size is 4 mm².
Why do I see mil in the results?
A mil is one thousandth of an inch, the unit used for wire diameters in the AWG standard. The table gives the diameter in mil and in mm.
Can I type a cross-section to find the AWG?
Yes. Type a value with mm² after it, such as 2.5 mm², and the calculator gives the nearest AWG number and its area.
Sources
- Wikipedia: American wire gauge (the ASTM B258 diameter formula and table)
- Wikipedia: IEC 60228 (standard conductor cross-sections)
Figures and text last checked on Tuesday, November 10, 2026.