Copper vs Aluminum Wire: Weight, Ampacity, and When to Use Each

Copper and aluminum are the two conductors used in virtually all electrical wiring. Copper is standard for residential branch circuits. Aluminum handles most utility distribution, service entrances, and large feeders. The tradeoff is weight, cost, and handling characteristics — and misunderstanding when to use each has caused real-world safety issues that led to specific NEC requirements.

Our  and wire gauge calculator handle weight and ampacity calculations for both materials.

Density comparison

Material	Density (lbs/ft3)	Density (g/cm3)
Copper (annealed)	559	8.96
Aluminum (1350 electrical alloy)	169	2.71
Ratio	Aluminum is 30% the weight of copper

Aluminum is roughly one-third the weight of copper — a decisive advantage for overhead power transmission and long feeder runs where conductor weight causes sag and mechanical stress.

Why aluminum needs a larger gauge

Copper has about 61% higher electrical conductivity than aluminum. Aluminum wire must be one to two AWG sizes larger than copper for equivalent ampacity.

Ampacity (75C, NEC 310.16)	Copper gauge	Aluminum gauge
30A	#10	#8
40A	#8	#6
55A	#6	#4
75A	#4	#2
100A	#1	#2/0
150A	#2/0	#4/0
200A	#3/0	350 kcmil

Weight comparison for equivalent ampacity

Despite needing a larger gauge, aluminum wins on weight at large conductor sizes:

200A service conductor	Size	Weight per foot
Copper #3/0	0.410" diameter	0.507 lbs/ft
Aluminum 350 kcmil	0.668" diameter	0.397 lbs/ft

The aluminum conductor is 22% lighter than copper for the same 200A capacity. For a 100-ft service entrance run, that is about 11 lbs lighter — meaningful overhead. At small gauges, copper wins: a #12 copper (15A) weighs less than the #10 aluminum needed to match it, which is why copper remains standard for residential branch circuits.

Cost comparison

Aluminum costs roughly 30-40% of copper per pound, and you need less weight for equivalent ampacity. For large conductors, aluminum is dramatically cheaper:

• 350 kcmil aluminum vs 3/0 copper for a 200A service: aluminum is approximately 60-70% cheaper
• For 200 linear feet of 200A service entrance conductors (3 wires), the savings can be $300-600

The aluminum branch circuit safety issue

In the 1960s and 70s, solid aluminum was used for residential branch circuit wiring (below #6) as a cost-saving measure during high copper prices. By the 1980s, significant fire risk was identified. The problem was not aluminum's conductivity but its terminations:

• Aluminum oxidizes readily, and aluminum oxide is electrically resistive
• Aluminum expands and contracts more than copper with temperature changes
• Connections at outlets and switches loosened over time, creating arcing and fire risk

NEC now requires special handling for aluminum branch circuit wiring:

• Aluminum branch circuits (#6 and smaller) must terminate on CO/ALR rated devices (outlets, switches)
• Panel lugs and breakers must be rated for aluminum
• Anti-oxidant compound is required at connections
• Pigtailing to copper with approved connectors (AlumiConn or Ideal In-Sure) is an accepted remediation for existing aluminum branch circuits

When to use each

Application	Preferred conductor	Reason
Branch circuits (#14, #12, #10)	Copper	Easier terminations, no special requirements, modest cost difference
Large appliance circuits (30-60A)	Either	Aluminum acceptable with proper AL-rated devices
Service entrance (100-400A)	Aluminum	Significant cost and weight savings; proper lugs always required
Feeders to subpanels (100A+)	Aluminum	Standard industry practice for conductors #4 and larger
Overhead utility spans	Aluminum (ACSR)	Weight advantage essential over long spans

For wire sizing, ampacity lookup, and weight calculations for any conductor material and gauge, use the wire gauge calculator. For material weight by length and shape, use the  or .