The standard wire gauge sizing chart for US residential and commercial branch circuits is governed by NEC Table 310.16. For a standard 15A circuit, use 14 AWG copper; for a 20A circuit, use 12 AWG copper; and for a 30A circuit, use 10 AWG copper. However, picking the right wire requires more than just matching the breaker size—you must account for insulation temperature ratings, conductor material, and installation conditions.

How to Read the NEC Wire Gauge Sizing Chart

Before jumping to the numbers, you must understand which column applies to your specific installation. The NEC table separates conductors by material (Copper vs. Aluminum) and by temperature rating (60°C, 75°C, and 90°C).

Which column applies to you? According to NEC 110.14(C), for circuits rated 100A or less, or for conductors sized 14 AWG through 1 AWG, you must use the 60°C column to determine ampacity unless the equipment terminals are explicitly marked otherwise. Most standard residential breakers and receptacles are rated for 75°C, but the 60°C rule acts as a safety baseline for smaller wires. The 90°C column is almost never used for final ampacity; it exists primarily as a starting point for derating calculations.

The Master Wire Gauge Sizing Chart (NEC Table 310.16)

Below is the complete ampacity table for common building wires (THHN, THWN-2, XHHW, and NM-B). Source: National Electrical Code (NFPA 70), Table 310.16.

Bookmark Quick-Jump Rows: 14 AWG (15A) | 12 AWG (20A) | 10 AWG (30A) | 8 AWG (40A) | 6 AWG (55A/65A) | 4 AWG (70A/85A) | 2 AWG (95A/115A)

AWG Size Copper 60°C (Amps) Copper 75°C (Amps) Copper 90°C (Amps) Aluminum 75°C (Amps) Standard Max Breaker
14 AWG152025N/A15A
12 AWG202530N/A20A
10 AWG303540N/A30A
8 AWG4050554040A / 50A*
6 AWG5565755050A / 60A*
4 AWG7085956570A / 80A
3 AWG851001107580A / 100A
2 AWG951151309090A / 110A
1 AWG110130145100110A / 125A
1/0 AWG125150170120125A / 150A
2/0 AWG145175195135150A / 175A
3/0 AWG165200225155175A / 200A
4/0 AWG195230260180200A / 225A

*Note: NEC 240.4(B) allows the next standard breaker size up if the calculated load does not exceed the wire ampacity, provided the breaker is under 800A. Always verify terminal temperature ratings.

Derating Factors and Voltage Drop: What the Chart Cannot Tell You

The wire gauge sizing chart above assumes ideal conditions: an ambient temperature of 86°F (30°C) and no more than three current-carrying conductors in a single raceway. When real-world conditions deviate, you must apply derating factors.

How Derating Modifies the Base Value

If you pull four to six current-carrying conductors through a single conduit, NEC Table 310.15(C)(1) requires you to derate the ampacity to 80%. Here is where the 90°C column becomes useful.

Worked Example: You are running five 12 AWG THHN wires in a conduit for a multi-wire branch circuit.

  • Base 90°C ampacity for 12 AWG = 30A.
  • Derate for 5 conductors (80%): 30A × 0.80 = 24A.
  • Final adjusted ampacity is 24A. Since 24A is greater than the 20A breaker protecting the circuit, 12 AWG THHN is perfectly legal and safe here.
If you had 7 to 9 conductors (derated to 70%), 30A × 0.70 = 21A. Still safe for a 20A breaker. But if you had 10 to 20 conductors (derated to 50%), 30A × 0.50 = 15A. Your 12 AWG wire is now only rated for 15A, and you must either upsize to 10 AWG or reduce the breaker size.

What the table cannot tell you: This chart does not account for voltage drop over long distances, physical conduit fill limits, or terminal lug torque requirements. For runs exceeding 100 feet, calculate voltage drop to ensure it stays below 3% for branch circuits. A 120V circuit dropping 4% will deliver only 115V to the load, causing motors to overheat and electronics to brownout.

Wire Gauge Sizing Chart FAQ

What wire gauge sizing chart applies to THHN vs NM-B cable?

THHN and THWN-2 wires are rated for 90°C in dry and wet locations, respectively. However, NM-B (Romex) cable is explicitly limited to the 60°C column by NEC 334.80, regardless of the fact that the individual wires inside the sheath might technically have 90°C insulation. Therefore, a 12 AWG NM-B cable is strictly capped at 20A, while a 12 AWG THHN wire in conduit starts its derating math at 30A (90°C) before termination limits cap it at 20A or 25A.

How do I use a wire gauge sizing chart for a 50 amp breaker?

For a 50A breaker (common for EV chargers, subpanels, or heavy shop equipment), you need 6 AWG copper or 4 AWG aluminum. Looking at the 75°C column, 6 AWG copper is rated for 65A, which safely covers the 50A load. If you are using NM-B cable, the 60°C column limits 6 AWG to 55A, which is still legally sufficient for a 50A breaker. Always ensure the receptacle or hardwired terminal lugs are rated for the wire size and temperature you select.

Why does my wire gauge sizing chart show different ampacities for copper and aluminum?

Copper is a vastly superior conductor to aluminum. It has lower electrical resistance and higher thermal conductivity. To carry the exact same current without overheating, an aluminum conductor must be physically larger (thicker) than a copper conductor. For example, to safely carry 100A at 75°C, you need 3 AWG copper, but you must step up to 1 AWG aluminum. Furthermore, aluminum expands and contracts more than copper under thermal load, requiring specific anti-oxidant paste and precise torque settings to prevent terminal fires.

Can a wire gauge sizing chart account for voltage drop over 100 feet?

No. The NEC ampacity tables only address thermal limits (preventing the wire from melting or catching fire). They do not guarantee performance. If you are running a 20A, 120V circuit to a detached garage 150 feet away, 12 AWG copper will safely handle the heat, but the resistance of the wire will cause a voltage drop of roughly 7.5V (over 6%). To maintain a 3% drop or less, you must upsize the wire to 8 AWG or even 6 AWG copper, despite the breaker remaining at 20A.