Choosing the wrong wire gauge is one of the most common — and dangerous — electrical mistakes. Too thin a wire overheats, trips breakers, or starts fires. Too thick is wasteful and expensive. Here's everything you need to know about AWG wire sizing.

What Is AWG?

AWG stands for American Wire Gauge, a standardized system for measuring wire diameter used primarily in the US and Canada. The system dates back to 1857 and is based on the number of drawing operations needed to produce a wire — more draws = thinner wire = higher AWG number.

How AWG Numbers Work

The AWG scale runs from 0000 (4/0) — the thickest common wire at 0.46 inches — to 40 AWG, which is thinner than a human hair. For household wiring, you'll typically work with 14 AWG through 6 AWG.

Matching Wire Gauge to Breaker Size

This is critical for safety. The wire gauge must match the circuit breaker to prevent the wire from overheating before the breaker trips:

• 15A breaker → 14 AWG (minimum)
• 20A breaker → 12 AWG (minimum)
• 30A breaker → 10 AWG (minimum)
• 40A breaker → 8 AWG (minimum)
• 50A breaker → 6 AWG (minimum)

Copper vs. Aluminum Wire

Aluminum wire has higher resistance than copper, so it requires a larger gauge for the same current. Aluminum is commonly used for service entrance wiring and large feeder circuits because it's cheaper and lighter.

• Copper 12 AWG → 20A
• Aluminum 10 AWG → 20A (must upsize by ~2 gauges)

Wire Length and Voltage Drop

For long runs (over 50 feet), you may need to increase wire gauge to prevent voltage drop — the loss of voltage over distance due to resistance. A 3% voltage drop is acceptable for lighting; 5% maximum for motor loads.

For example, a 20A circuit running 100 feet on 12 AWG copper might experience 3–5% voltage drop. Upsizing to 10 AWG would reduce that to under 2%.

Quick Reference: Home Circuit Sizing