Guides & Wire Size References
In-depth articles for electrical engineers, electricians, and students: how AWG sizes are derived, conductor classes, circular mils, plus detailed per-gauge reference sheets with ASTM B258 and IEC 60228 tables.
Featured guides
5 in-depth guides · Wire sizing fundamentals
Circular Mils Explained: cmil, kcmil and MCM
What circular mils are, why the unit exists (to cancel pi in round-conductor area math), how to convert cmil to mm², and the difference between kcmil and the older MCM label on North American cables.
Why AWG and Metric Wire Sizes Never Line Up
12 AWG converts to 3.31 mm² but you cannot buy a 3.31 mm² cable. Why the two systems are fundamentally different, how to round safely, and which four gauge sizes genuinely pass a metric resistance limit.
Conductor Classes 1, 2, 5 and 6 Explained
IEC 60228 Classes 1 (solid), 2 (stranded), 5 and 6 (flexible) — what the class number actually means, when to use each one, the minimum wire counts, and how stranded resistance limits vary with class.
AWG Diameter vs Cross-Section: Two Different Answers
Why 12 AWG has both a 2.05 mm diameter AND a 3.31 mm² label — which one to use for ferrules/glands vs cable sizing vs purchase orders, and the stranded-wire trap that catches everyone.
American Wire Gauge: How AWG Sizes Are Derived
The geometric series behind AWG — the two fixed points (4/0 = 460 mils, 36 AWG = 5 mils), the 1.1229 step ratio, formula to compute any gauge, and the 3-6-10 shortcuts for on-site estimation.
AWG Gauge References
16 per-gauge reference sheets · Diameter, mm², kcmil, applications
1/0 AWG in mm: Why Rounding Up Costs 31% Here
1/0 AWG in mm is 8.25 mm across, with a cross-section of 53.5 mm². Rounding up costs 31% more copper here, and the size below meets the resistance limit.
10 Gauge Wire in mm: Diameter, mm2 & Ampacity
10 gauge wire in mm is 2.59 mm across, with a cross-section of 5.26 mm2. Here is the metric size to order, the ampacity, and why 30 A caps it regardless.
12 Gauge Wire in mm: Diameter, mm2 & What to Order
12 gauge wire in mm is 2.05 mm across, with a cross-section of 3.31 mm2. Here is the metric cable that replaces it, and why 12 AWG fails a 4 mm2 spec.
14 Gauge Wire in mm and mm2: Diameter and Cable Size
14 gauge wire in mm is 1.63 mm across, with a cross-section of 2.08 mm2. Here is the metric cable to order and the 28% gap if you round the wrong way.
16 Gauge Wire in mm: Diameter and Conductor Size
16 gauge wire in mm is 1.29 mm across for solid wire. Here is the diameter, the metric size that replaces it, and why stranded 16 AWG measures much wider.
18 Gauge Wire in mm: Diameter, mm2 & Cable Size
18 gauge wire in mm is 1.02 mm across, with a cross-section of 0.823 mm2. It sits closer to a metric size than any other gauge, and that changes the choice.
2/0 AWG in mm: The Feeder Size That Converts Cleanly
2/0 AWG in mm is 9.26 mm across, with a cross-section of 67.4 mm2. It is one of only two gauges that meets the resistance limit of the metric size above it.
2 Gauge Wire in mm: Diameter, mm2 & Cable Size
2 gauge wire in mm is 6.54 mm across, with a cross-section of 33.6 mm2. It is one of only two gauges that actually meets its metric cable resistance limit.
20 Gauge Wire in mm: The One Time You Round Down
20 gauge wire in mm is 0.813 mm across, with a cross-section of 0.519 mm2. This is the one gauge where rounding down to the smaller metric size is correct.
24 Gauge Wire in mm: Diameter and Why mm2 Fails
24 gauge wire in mm is 0.511 mm across, with a cross-section of 0.205 mm2. The nearest metric size is more than double, so there is no real equivalent.
26 Gauge Wire in mm: Diameter and Metric Equivalent
26 gauge wire in mm is 0.404 mm across, with a cross-section of 0.128 mm2. The smallest metric size is almost four times larger, so there is no equivalent.
3/0 AWG in mm: Diameter, mm2 & the Metric Size
3/0 AWG in mm is 10.404 mm across, with a cross-section of 85 mm2. Here is the metric size to order, the ampacity, and how to read the 0-series numbering.
4/0 AWG in mm: Diameter, mm2 & Termination Size
4/0 AWG in mm is 11.684 mm across, with a cross-section of 107.2 mm2. Here is the metric size, the ampacity, and why the lug diameter is the number that bites.
4 Gauge Wire in mm: Diameter, mm2 & Ampacity
4 gauge wire in mm is 5.19 mm across, with a cross-section of 21.1 mm2. Here is the metric size to order, the ampacity, and where the two standards disagree.
6 Gauge Wire in mm: Diameter, mm2 & Ampacity
6 gauge wire in mm is 4.11 mm across, with a cross-section of 13.3 mm2. Here is the metric size to order, the ampacity, and how fast grouping erodes it.
8 Gauge Wire in mm: Diameter, mm2 & Ampacity
8 gauge wire in mm is 3.26 mm across, with a cross-section of 8.37 mm2. Here is the metric size to order, the ampacity, and the 28% cost of rounding down.