AWG to mm² converter

AWG to mm² — formula and table

AWG dimensions come from ASTM B258: diameter in mm = 0.127 × 92^(36−n)/39, where n is the gauge number (4/0 = −3, 3/0 = −2, 2/0 = −1, 1/0 = 0). Area follows from the circle: mm² = π/4 × d². Kcmil = circular mils ÷ 1000, and 1 kcmil = 0.5067 mm² exactly. The converter above runs these identities in both directions and rounds to the nearest gauge when you start from mm².

Field reality: the converted number is never what you buy

12 AWG converts to 3.31 mm² — but no cable is manufactured in 3.31 mm². Metric cable follows the IEC 60228 series (1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120 …), so the converter rounds up to the smallest standard size that is not smaller (4 mm² for 12 AWG, +21% copper). Cable is verified by DC resistance per kilometre, not by measuring copper: 12 AWG at ~5.21 Ω/km clears the 2.5 mm² limit (7.41 Ω/km) but the safe order is 4 mm² (4.61 Ω/km limit).

Diameter vs area — which one do you need?

Diameter (mm) is for physical hardware: glands, ferrules, lug barrels, drill sizes, conduit fill. Area (mm²) is for documents: cable schedules, ampacity, voltage drop, purchase orders. Stranded cable of the same nominal size measures wider than solid (air between strands) — Class 5 flexible at 4 mm² runs 3.0 mm max vs 2.4 mm solid — so size glands from the manufacturer overall diameter, never the solid conversion figure.