Aluminum vs Copper Wire | Electrical Calcs

The short answer: copper carries more, aluminum costs less

Copper conducts about 61% better than aluminum for the same cross-section, so aluminum has to be one to two AWG sizes larger to carry the same amps. In exchange, aluminum costs a fraction of copper per amp and weighs about a third — which is exactly why the big stuff (services, feeders) is aluminum and the small stuff (branch circuits) is copper.

	Copper	Aluminum
Conductivity	~100% (ref)	~61%
Size for same amps	smaller	1–2 sizes up
Cost per amp	high	low
Weight	heavier	~⅓ of copper
Typical use	branch circuits	services / feeders

Aluminum vs copper wire size chart

The same amps in each metal, for the circuits people ask about most:

Circuit	Copper	Aluminum
20 A	12 AWG	10 AWG
30 A	10 AWG	8 AWG
50 A	6 AWG	4 AWG
100 A service	4 AWG	2 AWG
200 A service	2/0 AWG	4/0 AWG

Aluminum runs about one to two AWG sizes larger across the board. The 100 and 200 amp rows are dwelling-service sizes (NEC 310.12). For the full aluminum wire ampacity chart next to copper — every gauge and its amp rating in both metals — see our AWG ampacity chart.

One tip when you buy: you'll see aluminum mostly in SER, SEU, and URD cable (services, feeders, and underground runs), while copper dominates NM-B "Romex" and THHN branch wiring. The label on the reel tells you which metal you're holding.

Cost and weight: why services use aluminum

On a short branch circuit the price gap barely matters — but on a service entrance, a large feeder, or a long underground (URD) run, aluminum's lower cost per amp and roughly one-third the weight add up fast. Pound for pound, aluminum conductor typically runs well under half the price of copper, and on a long service lateral that can mean hundreds of dollars saved. That's why almost every modern 200 amp service and 400 amp service is fed with aluminum, while copper's premium is saved for branch circuits and tight conduit fills.

Is aluminum wiring safe?

It depends which aluminum — and this is where the fear comes from. Two very different things share the name:

Old solid branch-circuit aluminum (~1965–1973) — used for 15 and 20 amp receptacle and lighting circuits, it had real trouble at connections (the metal expands, oxidizes, and loosens over time), and carries a genuine fire history. If a home has it, don't ignore it: remediate with COPALUM crimps or AlumiConn connectors and have it inspected.
Modern AA-8000-series aluminum — the alloy used in today's feeders and services is different, doesn't share that history, and is fully NEC-approved. The wire feeding most 200 amp panels is aluminum, and it's safe.

⚠ If your house has old aluminum branch wiring

A plain wire-nut pigtail is not an approved fix for pre-1974 solid aluminum branch circuits. Use COPALUM or AlumiConn connectors, or have the circuits evaluated by a licensed electrician. Many insurers ask about it directly.

Terminations: where aluminum actually fails

Here's the truth the horror stories miss: aluminum is safe when it's terminated correctly (NEC 110.14). That means AL-rated devices and lugs — CO/ALR-rated receptacles and switches for 15–20 amp branch aluminum — plus anti-oxidant where specified and the correct torque on every lug. Never land aluminum on a copper-only (CU) terminal. And to join copper to aluminum, use a connector listed for both (marked AL/CU) — direct contact of the two metals corrodes. Most aluminum failures are bad connections, not bad wire.

When to use copper vs aluminum

A quick decision:

Use copper for branch circuits, receptacles and lighting, most 15–60 amp appliance circuits, tight conduit, and anywhere the terminals are copper-only.
Use aluminum for the service entrance, large feeders, 100–400 amp services, and long underground (URD) runs — the cost and weight savings are real at that scale.

Common aluminum-vs-copper mistakes

The big one is sizing aluminum like copper — it needs to go up one to two sizes, or it's undersized and overheats. Others: landing aluminum on a CU-only terminal; skipping anti-oxidant or correct torque; "fixing" old branch aluminum with a plain wire nut instead of COPALUM/AlumiConn; assuming all aluminum is the dangerous kind; and joining copper to aluminum without an AL/CU-rated connector. Terminations, not the metal, are where things go wrong.

Copper and aluminum sizes by circuit

Both metals, for the circuits and services in this guide:

20 amp → 12 Cu / 10 Al. See 20 amp wire size.
30–60 amp → 10–6 Cu / 8–4 Al. See 50 amp and 60 amp.
100 amp service → 4 Cu / 2 Al. See 100 amp service.
200 amp service → 2/0 Cu / 4/0 Al. See 200 amp service.
Ground wire in both metals — see the ground wire size guide.

Frequently asked questions

Wire & CircuitIs aluminum wire as good as copper?

Aluminum carries less per size, so it runs one to two AWG sizes larger for the same amps. But it costs far less and weighs about a third, and it works well when sized and terminated correctly — which is why services and feeders use it.

⚡ Wire Size calculator →

ConversionsWhat is the aluminum equivalent of a copper wire size?

About one to two AWG sizes larger. For example, 12 copper is 10 aluminum, 6 copper is 4 aluminum, and 2/0 copper is 4/0 aluminum for a 200 amp service.

Code & SafetyIs aluminum wiring safe?

Modern AA-8000 aluminum in feeders and services is safe and NEC-approved. The fire history is about old solid aluminum branch-circuit wiring from about 1965 to 1973, which should be remediated with COPALUM or AlumiConn connectors.

Code & SafetyWhy do services use aluminum instead of copper?

For large conductors, aluminum costs a fraction of copper per amp and weighs about a third, so it is far cheaper and easier to handle on service entrances, feeders, and long underground runs.

Code & SafetyCan I connect copper and aluminum wire together?

Only with a connector listed for both metals (marked AL/CU), plus anti-oxidant where required. Direct contact between copper and aluminum corrodes and can overheat, so never just twist them together.

Wire & CircuitWhat size aluminum wire for a 200 amp service?

4/0 aluminum for a 200 amp dwelling service (the copper equivalent is 2/0), under the NEC 310.12 dwelling rule. Aluminum is the standard, cost-effective choice at that size.

Code & SafetyDo I need special outlets for aluminum wire?

For 15 and 20 amp branch circuits in aluminum, yes — use CO/ALR-rated receptacles and switches designed for aluminum, with correct torque and anti-oxidant where specified.

Wire & CircuitWhy is aluminum wire bigger than copper for the same amps?

Aluminum is only about 61% as conductive as copper, so it needs roughly 1.6 times the cross-sectional area to carry the same current — which works out to one or two AWG sizes larger.

Dr. Artie Vance

Technical reviewer · Ph.D. in Physics, MIT · 14 years' experience · Cross-checked against NEC 2026 & 2026

This guide is for general information based on the National Electrical Code and CPSC guidance. Conductor and termination rules vary by NEC edition and your local authority having jurisdiction (AHJ), and aluminum branch-circuit remediation is specialized work. Electrical work can be dangerous, so when in doubt, hire a licensed electrician.