Two ways to size a wire
mm², used in most of the world, is the cross-sectional area of the conductor, set out in standard sizes such as 1.5, 2.5, 4 and 6 mm². A bigger number is a thicker wire.
AWG (American Wire Gauge), used in North America, is a numbered scale where a bigger number is a thinner wire. It runs from 40 up to 0, then 1/0 to 4/0 for the thickest cables.
How the AWG scale works
- Every 3 gauges smaller, the area roughly doubles: 14 AWG has about twice the area of 17 AWG.
- Every 6 gauges smaller, the diameter roughly doubles.
- The diameter in mm is 0.127 × 92(36 − AWG) ÷ 39.
Common equivalents
- 18 AWG = 0.82 mm² (nearest metric: 0.75 or 1 mm²)
- 16 AWG = 1.31 mm² (nearest: 1.5 mm²)
- 14 AWG = 2.08 mm² (nearest: 2.5 mm²)
- 12 AWG = 3.31 mm² (nearest: 4 mm²)
- 10 AWG = 5.26 mm² (nearest: 6 mm²)
- 8 AWG = 8.37 mm² (nearest: 10 mm²)
Converting safely
The two series do not line up exactly, so when replacing one with the other always round up to the next larger size: a wire that is too thin carries less current and drops more voltage. A circuit designed for 14 AWG gets 2.5 mm², not 1.5 mm².
Size is not the whole story
How much current a wire may carry also depends on its insulation, how it is installed and how many wires run together, and wiring rules set those limits. Long runs need a larger size again to keep the voltage drop small.
Tools
The Wire Gauge Chart lists every AWG size with its diameter, mm² and resistance. The Cable Size Calculator picks a size for a current, length and voltage drop, and the Voltage Drop Calculator checks a size you already have.