Wire Gauge Converter
American Wire Gauge (AWG) is the US standard for copper wire diameter. The diameter formula is defined in ASTM B258: diameter (inches) = 0.005 * 92^((36-AWG)/39). This converter takes an AWG number and calculates the exact diameter in inches and millimeters, cross-sectional area in mm2, and resistance per unit length. It also supports entering a diameter in mm to find the nearest AWG. AWG 0000 (called 4/0) is the thickest at 11.684 mm; AWG 40 is the thinnest at 0.0799 mm.
AWG diameter formula (ASTM B258)
d (inches) = 0.005 * 92^((36-AWG)/39)
Cross-section (mm2) = pi * (d_mm / 2)^2. Copper resistivity = 1.724e-8 ohm-m (NIST), so resistance (ohm/km) = 1.724e-8 * 1000 / (area_m2). For 0/n gauge wires, AWG is expressed as negative: 4/0 = AWG -3, 3/0 = AWG -2, 2/0 = AWG -1, 1/0 = AWG 0.
Common AWG reference values
- AWG 4/0 (-3): Diameter 11.684 mm, area 107.2 mm2. Heavy power transmission.
- AWG 2: Diameter 6.544 mm, area 33.6 mm2. Service entrance, large motors.
- AWG 10: Diameter 2.588 mm, area 5.26 mm2. 30-amp circuits (US).
- AWG 12: Diameter 2.053 mm, area 3.31 mm2. 20-amp circuits (US).
- AWG 14: Diameter 1.628 mm, area 2.08 mm2. 15-amp circuits (US).
- AWG 22: Diameter 0.644 mm, area 0.326 mm2. Signal wiring, thermostat wire.
Wire gauge converter: frequently asked questions
How is AWG diameter calculated?
AWG diameter in inches = 0.005 * 92^((36-AWG)/39). The formula is exact for AWG 0 through 36, defined by ASTM B258. To convert to millimeters, multiply by 25.4 (exact). AWG 0000 (4/0) has diameter 0.46 inches = 11.684 mm.
Why do higher AWG numbers mean thinner wire?
AWG was originally defined by the number of drawing operations needed to produce the wire. More draws produce thinner wire. AWG 40 is extremely fine (used in microelectronics), while AWG 0000 (4/0) is very thick cable used for heavy power distribution.
How does AWG relate to mm2 cross-section?
Cross-sectional area in mm2 = pi * (d/2)^2 where d is diameter in mm. AWG 14 (common household wiring in the US) has diameter 1.628 mm and cross-section 2.08 mm2. The European equivalent is the nearest standard cable size (2.5 mm2 for AWG 14).
What is the AWG for common household wiring?
Standard US residential wiring: AWG 14 (15-amp circuits), AWG 12 (20-amp circuits), AWG 10 (30-amp circuits, dryers and ovens). The NEC sets ampacity limits based on AWG and insulation type. This calculator shows diameter and area only, not ampacity.
What is the difference between AWG and SWG?
AWG (American Wire Gauge) is the US standard. SWG (Standard Wire Gauge) is the British standard, now largely superseded by IEC metric cross-sections. For the same gauge number, AWG and SWG wires have different diameters. This converter handles AWG only.
Official sources
- NIST CODATA: Electrical resistivity of copper.
- NIST SP 811: Inch-to-mm conversion factor.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.