AWG Wire Gauge: Diameter, Cross-Section Area, and Typical Ampacity
October 29, 2026
American Wire Gauge (AWG) is a standardized system for the diameter of round, solid, electrically conducting wire. A counterintuitive feature is that a higher gauge number means a thinner wire. The scale is logarithmic: each decrease of 6 gauge numbers doubles the diameter, and every 3 gauge numbers halves or doubles the cross-sectional area. The formula for the diameter in inches is d = 0.005 × 92^((36 − n) ÷ 39), where n is the gauge number. For 12 AWG, d = 0.005 × 92^(24/39) = 0.0808 inches, or 2.053 mm.
Gauge determines resistance and how much current a wire can carry safely, so choosing the right gauge is essential in electrical work. This article provides conversion data and general information. Always follow the electrical code and consult a qualified electrician for installations.
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Values are for solid copper conductors. Resistance per 1,000 feet at 20°C is approximately 1.0 ohm for 10 AWG, 1.6 for 12 AWG, 2.5 for 14 AWG, 4.0 for 16 AWG, and 6.4 for 18 AWG, rising as the wire gets thinner. The typical ampacities shown are the maximum current ratings for the common overcurrent protection in building wiring in the US (NEC): 30 A for 10 AWG, 20 A for 12 AWG, 15 A for 14 AWG, with 16 and 18 AWG for appliance cords and low-voltage wiring and not for branch circuits.
| AWG | Diameter (in) | Diameter (mm) | Area (mm²) | Typical breaker limit (building wire) |
|---|---|---|---|---|
| 10 | 0.1019 | 2.588 | 5.26 | 30 A |
| 12 | 0.0808 | 2.053 | 3.31 | 20 A |
| 14 | 0.0641 | 1.628 | 2.08 | 15 A |
| 16 | 0.0508 | 1.291 | 1.31 | Appliance cords, low voltage |
| 18 | 0.0403 | 1.024 | 0.82 | Lamp cords, low voltage |
Metric Equivalents
Outside North America, wire is specified by cross-sectional area in square millimeters. 12 AWG (3.31 mm²) is approximately 2.5 or 4 mm² in the European system; 14 AWG (2.08 mm²) is close to 1.5 or 2.5 mm². The conversion is not exact, so use the appropriate local standard. To convert gauge to area: A = π/4 × d²; for 12 AWG, π/4 × 2.053² = 3.31 mm². The rule of 3s: increasing the gauge number by 3 halves the area and doubles the resistance per length; going from 12 to 15 AWG halves the cross-section.
Current, Voltage Drop, and Length
Ampacity depends on insulation temperature rating, ambient temperature, bundling, and installation method, so the numbers in tables are for specific conditions. Voltage drop over a long run matters too. For a 12 AWG circuit carrying 16 A over 100 feet one way (200 feet of wire in total), the resistance is 1.6 ohm per 1,000 feet × 0.2 = 0.32 ohm, and the drop is 16 × 0.32 = 5.1 volts, or 4.3% of 120 V, above the commonly recommended limit of 3%. Using a thicker wire, 10 AWG (1.0 ohm per 1,000 feet), reduces the drop to 3.2 volts, or 2.7%. Long runs to outbuildings, pumps, and EV chargers often require upsizing the wire.
Stranded Wire and Practical Notes
Stranded wire of the same AWG has a slightly larger overall diameter due to gaps between strands, but the same conductor cross-section. Use the right connectors and stripping tools for each gauge. Do not replace a breaker with a larger one without upgrading the wire. Aluminum wire is less conductive and typically requires a larger size than copper for the same current. Never exceed the rating of the wire or the device. When in doubt, hire a licensed electrician.
Frequently Asked Questions
Does a higher AWG number mean thicker wire?
No. A higher number means thinner wire.
What is the diameter of 12 AWG wire?
About 2.05 mm (0.0808 inch).
How does area change with gauge?
Every 3 gauge numbers halves or doubles the area, and every 6 doubles or halves the diameter.
What gauge wire is used for a 20 amp circuit?
12 AWG copper in typical US building wiring.
Why does long wire need a thicker gauge?
To limit voltage drop caused by the wire's resistance.