AWG Wire Diameter Chart: Sizes, Ampacity, and NEC 310.16 Reference

The American Wire Gauge (AWG) system is a logarithmic stepped standard used to specify the physical diameter and cross-sectional area of round, solid, non-ferrous electrical wire. Because it is an inverse scale, a smaller AWG number means a larger physical diameter and higher current-carrying capacity. For a direct answer: a standard 14 AWG copper wire has a bare conductor diameter of 0.0641 inches (1.628 mm), while a 12 AWG wire measures 0.0808 inches (2.053 mm). Every time you drop down three gauge sizes (e.g., from 12 AWG to 9 AWG), the cross-sectional area exactly doubles. Every six gauge drops doubles the physical diameter.

Knowing the bare awg wire diameter is critical for calculating conduit fill, verifying voltage drop, and ensuring your lugs can physically clamp the conductor. Below is the master reference chart combining physical dimensions with allowable ampacities.

The Master AWG Wire Diameter & Ampacity Chart

Which Column Applies to Your Installation?

A common and dangerous mistake on the jobsite is looking at a spool of 90°C THHN wire, seeing the 90°C ampacity column, and sizing the breaker based on that higher number. In almost all residential and light commercial applications, you cannot use the 90°C column for final overcurrent protection sizing.

NEC Section 110.14(C) dictates that the allowable ampacity is limited by the temperature rating of the terminations (the lugs on your breaker, panel, or receptacle), not just the wire insulation. This is known as the 'weakest link' rule.

• The 60°C Column: Use this for circuits rated 100 amps or less, or for conductors sized 14 AWG through 1 AWG, unless the equipment is explicitly marked for 75°C. Most standard residential receptacles and basic breakers fall here. This is why 14 AWG is capped at 15A and 12 AWG at 20A, even if the wire is THHN.
• The 75°C Column: Use this for circuits rated over 100 amps, or conductors sized larger than 1 AWG. Most modern commercial panels, subpanels, and heavy-duty appliances (like ranges and dryers) have 75°C rated lugs.
• The 90°C Column: You are generally only allowed to use this column for derating calculations (explained below) or when the entire assembly—including both termination points and the wire—is explicitly rated and marked for 90°C, which is exceedingly rare in standard building wiring.

Derating Factors: When Base Ampacity Drops

The ampacities in the table above assume ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together. When real-world conditions deviate, you must apply derating factors to prevent the wire from overheating and melting its insulation.

1. Bundling (More than 3 Current-Carrying Conductors):
When you pull multiple circuits through the same conduit, the wires heat each other up. Per NEC 310.15(C)(1), if you have 4 to 6 current-carrying conductors in a raceway, you must multiply the base ampacity by 80%. For 7 to 9 conductors, you multiply by 70%.

Worked Example: You are pulling three 120/240V multi-wire branch circuits (6 current-carrying conductors total: 3 hots, 3 neutrals) using 12 AWG THHN (90°C rated) in a single EMT conduit.
- Base 90°C ampacity for 12 AWG = 30A.
- Derating factor for 6 conductors = 80%.
- Adjusted ampacity = 30A × 0.80 = 24A.
However, per NEC 110.14(C), the final termination limit for a standard 20A breaker is the 60°C column (20A). Because 24A is greater than 20A, the wire is still legally permitted to be used on a 20A breaker. If you had 10 conductors (derate to 70%: 30A × 0.70 = 21A), you would still pass the 60°C termination check, but you are getting dangerously close to the limit.

2. High Ambient Temperatures:
If your conduit runs across a hot roof or through an unconditioned attic where temperatures regularly exceed 30°C (86°F), you must apply the temperature correction factors from the bottom of NEC Table 310.16. At 41-45°C (105-113°F), a 90°C THHN wire must be derated to 87% of its base value.

What This Table Cannot Tell You (Edge Cases & Code Limits)

While the awg wire diameter and base ampacity chart is the foundation of wire sizing, it omits three critical physical and electrical realities that will fail an inspection or cause equipment malfunction if ignored.

Voltage Drop Limits

NEC Table 310.16 tells you what size wire will prevent a fire, but it does not guarantee the equipment will actually run. For long runs (typically over 100 feet), you must calculate voltage drop using the DC resistance values found in NEC Chapter 8, Table 8. The NEC recommends a maximum 3% voltage drop on branch circuits and 5% total from the service entrance to the furthest outlet. A 12 AWG wire might be legally ampacious for a 20A circuit, but if it's 250 feet long to a shed, the voltage at the receptacle could drop below 110V, causing motors to overheat and trip their internal thermal protectors.

Conduit Fill Capacity

The bare diameters listed in the table do not include insulation thickness. To determine how many wires physically fit inside a PVC or EMT conduit, you must use the overall diameter (including insulation) and apply NEC Chapter 9, Table 1. For three or more wires in a conduit, the maximum allowable fill is 40% of the conduit's internal cross-sectional area. Trying to jam four 6 AWG THHN wires into a 1/2-inch EMT nipple will result in damaged insulation and a failed pull.

Aluminum vs. Copper Sizing

This chart is strictly for copper. If you are sizing aluminum conductors (common for service entrance feeders and subpanels due to cost), the physical diameter for a given AWG is identical, but the ampacity is significantly lower. As a rule of thumb, aluminum must be sized two AWG steps larger than copper to carry the same current (e.g., you must use 2 AWG aluminum to replace 4 AWG copper for a 100A feeder). Always verify aluminum ampacities using the specific aluminum columns in NEC Table 310.16, and ensure your terminations are explicitly rated for aluminum (marked 'AL' or 'AL/CU') to prevent galvanic corrosion and high-resistance arcing.