AWG Wire Size Chart: What the Numbers Mean and How to Use Them

American Wire Gauge (AWG) is the standard sizing system for copper and aluminum conductors in North American electrical work. If you've never dealt with it before, the first thing to know is that the numbers run backward: a 14 AWG wire is thinner than a 10 AWG wire. The smaller the gauge number, the larger the conductor.

This trips people up constantly, even experienced ones. It helps to know why: the AWG system is based on the number of drawing dies a wire passes through during manufacture. More draws means a thinner wire, so higher numbers correspond to smaller diameters.

What AWG numbers actually measure

AWG specifies the cross-sectional area of the conductor, not its diameter directly. The reference point is 0000 AWG (written 4/0), which is 0.46 inches in diameter. From there, the system steps down in a logarithmic progression. Each step of 3 gauge numbers roughly halves the cross-sectional area; each step of 6 roughly halves the diameter.

The practical implication is that resistance increases as the gauge number goes up. A 12 AWG copper conductor has about 1.59 ohms per 1,000 feet at 75°C. A 14 AWG conductor has about 2.53 ohms per 1,000 feet. That difference matters when you're calculating voltage drop across a long run.

Common wire sizes and their ampacity ranges

The table below covers the sizes you'll encounter in most residential and light commercial work. Ampacity values are for copper conductors at 60°C/75°C temperature ratings, in free air or conduit, per NEC Table 310.12. Use these as a starting estimate and verify against the full NEC table for your specific installation conditions.

These are for copper in conduit at 75°C. Aluminum conductors of the same gauge carry roughly 80% of the copper ampacity. Temperature rating of the insulation matters too: 60°C-rated wire has lower ampacity than 90°C-rated wire of the same gauge, though the NEC typically bases the final calculation on the lower of the insulation rating and the terminal rating.

How derating affects these numbers

The table above assumes normal conditions. Several factors reduce the usable ampacity:

Conduit fill. When multiple current-carrying conductors share a conduit, heat builds up. NEC 310.15(C)(1) requires derating: 4–6 conductors get 80% of the base ampacity, 7–9 get 70%, and so on.

Ambient temperature. The base ampacity assumes 30°C ambient. At 40°C, you apply a correction factor of about 0.88 for 75°C-rated conductors. In hot attics or near boilers, this matters.

Conduit type and burial. Underground conductors in conduit or direct burial have different tables.

A cable size calculator can apply these correction factors automatically once you enter your installation details, which saves a lot of table-hunting.

Reading the chart for a specific circuit

Say you're wiring a 30 A dryer circuit. You look at the table and see 10 AWG copper handles 30 A at 75°C. That's your minimum by ampacity.

But you're not done. If the circuit run is long, say 80 feet from panel to outlet, you also need to check voltage drop. At 30 A over 80 feet on 10 AWG copper, the round-trip drop on a 240 V single-phase circuit works out to roughly 2.7%, which is under the 3% guideline. If the run were 120 feet, you'd be over and would want to step up to 8 AWG.

Ampacity sets the floor. Voltage drop sometimes pushes you to the next size up.

Sizes above 4/0

For very large loads, AWG runs out at 4/0, and the system switches to kcmil (thousand circular mils). You'll see 250 kcmil, 350 kcmil, 500 kcmil on large service entrance conductors. These are outside the scope of this chart but follow the same principles: larger cross-section, lower resistance, higher ampacity.

These ampacity values are estimates based on NEC Table 310.12. Always verify your conductor sizing against the current NEC and your local jurisdiction's adopted code. A licensed electrician should review any permanent wiring installation.