AWG Wire Gauge Calculator
Convert American Wire Gauge (AWG) to mm², diameter, resistance, and maximum ampacity.
Essential for electrical projects and DIY wiring.
What Is AWG?
AWG stands for American Wire Gauge (also called Brown & Sharpe gauge), a standardized wire gauge system used in North America for electrically conductive wire. It was established in 1857. The system is counterintuitive at first: a higher AWG number means a thinner wire. AWG 40 wire is about the thickness of a human hair. AWG 0000 (four-ought) wire is about 11.7 mm in diameter — thick enough to carry hundreds of amps.
The Mathematical Formula Behind AWG
AWG is based on a logarithmic scale. The formula for diameter in millimeters is:
diameter (mm) = 0.127 × 92^((36 − AWG) / 39)
Every 6 AWG numbers, the wire diameter doubles. Every 3 AWG numbers, the wire cross-sectional area (and therefore current capacity) doubles. This geometric progression means that jumping from AWG 14 to AWG 8 gives you four times the cross-sectional area.
Why Does Wire Gauge Matter for Safety?
Resistance is the key. A thinner wire has higher resistance per unit length. When current flows through resistance, it generates heat (P = I²R). Too much current through too thin a wire causes the insulation to melt, potentially starting an electrical fire. This is why every circuit needs correctly sized wire AND a correctly sized breaker — the breaker must trip before the wire overheats.
NEC (National Electrical Code) Ampacity Requirements
The NEC sets maximum ampacity (current-carrying capacity) for wire in conduit at 60°C insulation temperature rating, which is the most conservative rating:
- AWG 14: 15 amps (standard 15A household circuit)
- AWG 12: 20 amps (kitchen appliance circuits)
- AWG 10: 30 amps (dryer, water heater)
- AWG 8: 40 amps (range, large A/C unit)
- AWG 6: 55 amps
- AWG 4: 70 amps
- AWG 2: 95 amps
Copper vs. Aluminum
Copper has lower resistivity (1.72×10⁻⁸ Ω·m) than aluminum (2.65×10⁻⁸ Ω·m), meaning copper wire can carry more current at the same gauge. Aluminum wire is cheaper and lighter, but requires larger gauge for the same ampacity, and special connectors to prevent oxidation at junctions. Most residential wiring uses copper. Large service entrance cables are often aluminum to reduce cost and weight.
Metric Equivalent (mm²)
In most of the world, wire is sold by cross-sectional area in mm². Common equivalents: AWG 14 ≈ 2.5 mm², AWG 12 ≈ 4 mm², AWG 10 ≈ 6 mm², AWG 8 ≈ 10 mm². When buying wire internationally, always check the mm² rating.