AWG Wire Gauge & Ampacity Chart: Wire Sizes, Amps & How to Choose

Every wiring question eventually comes down to one decision: what gauge? Too small and the conductor overheats, the breaker nuisance-trips, or worse. Too large and you have wasted money and made the pull harder than it needed to be. The right answer is set by three things — the current the wire must carry, the distance it runs, and whether it is copper or aluminum. (Ampacity figures here follow the NFPA 70 (NEC) Table 310.16; dimensions follow ASTM B258.)

This guide is the complete AWG reference: the master wire gauge chart, the NEC ampacity tables for copper and aluminum, the exact wire size you need for every common amperage from 15 A to 200 A, and a three-step method to choose correctly. Bookmark it — it is the chart you will come back to on every job.

The Quick Answer

Three rules cover almost every wire-sizing decision:

• Match the ampacity: pick the smallest wire whose rating meets the load (use the 75°C column of NEC Table 310.16 for most work).
• Mind the small-conductor rule: NEC 240.4(D) caps the breaker regardless of ampacity — 14 AWG → 15 A, 12 AWG → 20 A, 10 AWG → 30 A (copper).
• Aluminum goes up: aluminum carries less current than copper of the same gauge, so step up one or two sizes.

The lower the AWG number, the thicker the wire and the more current it carries. Everything else on this page is the detail behind those three rules.

What AWG Means

AWG stands for American Wire Gauge, the standard system for wire diameter used in the US and Canada, defined by ASTM B258. It is counterintuitive at first: the gauge number is inverse to the wire size. A 14 AWG wire is thinner than a 6 AWG wire, and a 4/0 ("four-aught") conductor is enormous.

The system follows a clean geometric progression, and two rules of thumb fall out of it that every electrician memorizes:

• Every 3-gauge decrease doubles the cross-sectional area and halves the resistance (e.g. 12 AWG → 9 AWG doubles the copper).
• Every 6-gauge decrease doubles the diameter and quadruples the area (e.g. 18 AWG → 12 AWG).

Cross-sectional area is what actually determines how much current a wire can carry. In North American codes it is expressed in circular mils (CM) — a circular mil is the area of a circle one thousandth of an inch in diameter. For sizes larger than 4/0, the unit switches to kcmil (thousands of circular mils), which is why you see "250 kcmil" instead of a gauge number on big feeders.

AWG Wire Size Chart (Diameter & Area)

The master reference. Diameter and circular mils come from the AWG standard; metric area is included for international readers.

Wire Ampacity Chart (NEC Table 310.16)

This is the table that matters most for sizing. Ampacity is the maximum current a conductor can carry continuously without exceeding its temperature rating. NEC Table 310.16 lists three temperature columns — 60°C, 75°C, and 90°C. Most installations are sized on the 75°C column, because terminations are rated 75°C per NEC 110.14(C). The 90°C column is generally used only for derating math, not final sizing.

Copper wire ampacity

Aluminum wire ampacity

Aluminum carries less current at the same gauge. Note how each aluminum size lands roughly one to two AWG behind copper.

Wire Size by Amperage

The fast lookup most people actually want: pick your breaker/load size, read the wire. Based on NEC Table 310.16 at 75°C, with the small-conductor rule applied.

How to Choose the Right Wire Size

Three steps turn the tables above into a correct, code-compliant choice:

1. Find the load and pick the column. Determine the circuit current in amps and the material (copper or aluminum). Use the 75°C column unless you have a specific reason not to.
2. Select the smallest wire that meets the ampacity, then apply the small-conductor rule (240.4(D)). The wire must satisfy both its ampacity and the breaker limit.
3. Check voltage drop and derating. On runs over ~50 ft, verify voltage drop stays under 3% (branch) or 5% (combined). Apply temperature and conduit-fill derating per NEC 310.15(B). Upsize if either pushes you over.

Copper vs Aluminum Wire Size

The single most common sizing question after "what gauge for X amps" is whether to use copper or aluminum. The trade-off:

• Aluminum needs to be 1–2 AWG larger for the same current, because it has about 60% more resistance than copper per unit size.
• Aluminum is cheaper per foot, often substantially — which is why service entrances and long feeders are frequently aluminum despite the larger size.
• Aluminum requires anti-oxidant paste (Noalox, Penetrox) at terminations and listed AL/CU-rated connectors. The old aluminum branch wiring from the late 1960s–70s is a known fire hazard; modern aluminum feeders, properly terminated, are not.
• Copper is standard for branch circuits, especially 8 AWG and smaller. Aluminum dominates large feeders and service entrances where the cost savings are biggest.

Voltage Drop & Long Runs

Ampacity keeps a wire from overheating, but it does not guarantee the load gets enough voltage. On long runs, resistance "drops" voltage along the wire — lights dim, motors run hot, electronics misbehave. The NEC recommends keeping voltage drop under 3% on a branch circuit and 5% combined.

The rule of thumb: for runs over about 50 feet, expect to upsize one gauge; over 100 feet, always run the numbers. The full method — the formula, K-values, and worked examples — is covered in our companion guide.

Common Wire Sizing Mistakes

• Sizing for ampacity only. A wire that won't overheat can still starve the load on a long run. Always check voltage drop past ~50 ft.
• Ignoring the small-conductor rule. 12 AWG copper is "rated" 25 A but legally limited to a 20 A breaker (240.4(D)). Putting it on a 25 A breaker is a code violation.
• Reading the wrong temperature column. Sizing off the 90°C column gives optimistic numbers; final sizing uses 75°C because of termination ratings (110.14(C)).
• Swapping copper and aluminum ratings. Aluminum carries less — using copper ampacity for an aluminum wire undersizes it by one to two gauges.
• Forgetting derating. More than 3 current-carrying conductors in a raceway, or high ambient temperature, reduces ampacity per NEC 310.15(B).
• Confusing a service with a branch circuit. The dwelling-service allowance (310.12) lets services use smaller wire — but it does not apply to ordinary branch circuits or feeders.
• Aluminum on the wrong terminations. Aluminum requires listed AL/CU connectors and anti-oxidant paste; standard copper-only lugs are not rated for it.

Key Takeaways

• Smaller AWG number = thicker wire = more current. Every 3-gauge drop doubles the copper area.
• Copper at 75°C: 14 AWG = 15 A, 12 AWG = 20 A, 10 AWG = 30 A, 8 AWG = 40–50 A, 6 AWG = 55–65 A (with 240.4(D) applied).
• Aluminum carries less — step up one or two AWG sizes versus copper.
• Size on the 75°C column (NEC Table 310.16) for most work; use 90°C only for derating math.
• The small-conductor rule (240.4(D)) caps the breaker on 14/12/10 AWG regardless of raw ampacity.
• Dwelling services get a break: NEC 310.12 allows smaller wire (e.g. 2/0 Cu or 4/0 Al for 200 A).
• Always check voltage drop on runs over ~50 ft and apply derating for heat and conduit fill.