American Wire Gauge Sizes and Properties Chart: Resistance & Ampacity Reference

When sizing conductors for a branch circuit, feeder, or low-voltage DC run, guessing is not an option. The American Wire Gauge (AWG) system is logarithmic: every decrease of 3 gauge numbers doubles the cross-sectional area, and every decrease of 10 gauge numbers multiplies the area by exactly 10. But knowing the physical diameter is only half the battle. To prevent melted insulation or nuisance breaker trips, you need to cross-reference physical properties (resistance) with thermal limits (ampacity).

Below is the master reference for American wire gauge sizes and properties chart resistance and thermal ampacity. This data synthesizes physical dimensions from NEC Chapter 9, Table 8 with the allowable ampacities defined in NEC Table 310.16.

The Master AWG Reference Chart (NEC 310.16 & Chapter 9)

Use the quick-jump links below to skip to the most frequently queried sizes for residential and light commercial work: 14 AWG | 12 AWG | 10 AWG | 6 AWG | 2 AWG | 4/0 AWG.

*Note on small conductors: Per NEC 240.4(D), the overcurrent protection for 14, 12, and 10 AWG copper is strictly limited to 15A, 20A, and 30A respectively, regardless of the higher values shown in the 75°C or 90°C columns, unless specific motor or welder exceptions apply.

Which Column Applies to Your Installation?

The most common mistake DIYers and junior apprentices make is looking at a spool of 90°C-rated THHN wire, reading the 90°C column, and sizing the breaker accordingly. In almost all standard residential and commercial applications, you cannot use the 90°C column for final breaker sizing.

To determine which column governs your installation, you must look at the weakest link in the circuit: the termination points (breakers, lugs, receptacles). NEC Article 110.14(C) dictates the rules for termination temperature limits:

• The 60°C Column: Use this column if your equipment is rated 100 Amps or less, and the manufacturer has not explicitly marked a higher temperature rating on the lug. Most standard residential receptacles and older breakers fall into this category. Even if you pull 90°C THHN wire, if it lands on a 15A/20A receptacle rated for 60°C, your allowable ampacity is capped at the 60°C value.
• The 75°C Column: Use this column for equipment rated over 100 Amps, or for equipment explicitly marked as 75°C rated (which includes most modern commercial breakers, subpanel lugs, and heavy-duty receptacles).
• The 90°C Column: This column is almost exclusively used as the starting point for derating calculations (explained below). You can only use the 90°C ampacity for final sizing if every single termination point in the entire circuit—including the breaker, the splice connectors, and the device lugs—is explicitly rated and marked for 90°C, which is exceptionally rare in standard building wiring.

How Derating Modifies Base Values (And What the Table Can't Tell You)

The ampacities in the chart above assume ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together in a single raceway or cable. When real-world conditions deviate, you must apply correction and adjustment factors.

Calculating Bundling Derating

When you pull more than three current-carrying conductors through a single conduit, the heat generated by the wires cannot dissipate efficiently. NEC Table 310.15(C)(1) requires you to 'derate' the ampacity. You apply this derating factor to the 90°C column, then compare the result to your termination limit.

Worked Example: You are pulling four current-carrying 12 AWG THHN (90°C) conductors through a single EMT conduit to feed two multi-wire branch circuits. Your breakers and receptacles are standard 75°C rated.

1. Base Value: Look at the 90°C column for 12 AWG = 30A.
2. Derating Factor: 4 to 6 conductors requires an 80% adjustment factor.
3. Adjusted Ampacity: 30A × 0.80 = 24A.
4. Termination Check: Your terminations are 75°C. The 75°C column for 12 AWG is 25A. Since 24A is less than 25A, the wire is thermally safe.
5. Final Overcurrent Protection: Per NEC 240.4(D), 12 AWG is capped at a 20A breaker anyway. You are clear to use a 20A breaker.

What This Table Cannot Tell You

While this American wire gauge sizes and properties chart covers thermal limits and DC resistance, it has blind spots that require separate calculations:

• Voltage Drop: The NEC ampacity tables do not account for voltage drop over long distances. A 12 AWG wire might be thermally safe carrying 20A at 100 feet, but the resistance (1.98 Ω/kft) will cause a voltage drop of roughly 7.9V on a 120V circuit (over the recommended 3% limit). For long runs, you must calculate voltage drop using the DC Resistance column and bump up the wire size accordingly.
• AC Impedance and Skin Effect: The resistance column lists DC resistance. For standard 60Hz AC power in sizes smaller than 2/0 AWG, AC impedance is nearly identical to DC resistance. However, for large feeders (like 500 kcmil or larger) or high-frequency applications (like VFD outputs or solar inverter outputs), AC skin effect and proximity effect increase the effective resistance. You must consult NEC Chapter 9, Table 9 for AC impedance values in those scenarios.
• Physical Lug Fit: The chart tells you that 4/0 AWG is rated for 195A at 60°C, making it technically sufficient for a 200A residential service panel if calculated under specific residential rules (NEC 310.12). However, many 200A main breaker lugs are physically designed to accept a maximum of 2/0 AWG or 3/0 AWG. Always verify the physical wire bending space and lug sizing on the equipment nameplate before purchasing large-gauge wire.

By treating this chart as the starting point—rather than the final word—you ensure your wiring is not only code-compliant and thermally safe, but also optimized for the actual electrical load and physical distance of your installation.