When sizing conductors for residential and commercial branch circuits, the direct answer for standard copper wire ampacities is: 14 AWG handles 15 amps, 12 AWG handles 20 amps, 10 AWG handles 30 amps, 8 AWG handles 40 amps, and 6 AWG handles 55 amps (or 65 amps at 75°C terminations). However, pulling a single number from memory is where dangerous mistakes happen. True ampacity depends entirely on the insulation type, the termination temperature ratings of your devices, and how many wires share the same raceway.

The definitive wire gauge amps chart used by electricians and inspectors in the United States is derived from NFPA 70 (National Electrical Code) Table 310.16. Below is the master reference for copper conductors, followed by the critical rules for applying these numbers to your actual installation.

The Master Wire Gauge Amps Chart (NEC Table 310.16)

How to read this table: The ampacity of a wire is not a single fixed number; it changes based on the thermal limits of the insulation and the equipment it connects to. The table below provides the allowable ampacities for copper conductors rated up to 2000 volts across three standard temperature columns: 60°C (140°F), 75°C (167°F), and 90°C (194°F). The final column lists the maximum standard overcurrent protective device (OCPD / breaker) size permitted by NEC 240.4(B) and 240.4(D).

Table 1: Copper Conductor Ampacities (Not more than three current-carrying conductors in raceway, 30°C ambient)
AWG / kcmil 60°C (140°F) Amps 75°C (167°F) Amps 90°C (194°F) Amps Max Standard Breaker
14 AWG 15 20 25 15A *
12 AWG 20 25 30 20A *
10 AWG 30 35 40 30A *
8 AWG 40 50 55 50A
6 AWG 55 65 75 70A
4 AWG 70 85 95 90A
3 AWG 85 100 110 110A
2 AWG 95 115 130 125A
1 AWG 110 130 150 150A
1/0 AWG 125 150 170 175A
2/0 AWG 145 175 195 200A
3/0 AWG 165 200 225 225A
4/0 AWG 195 230 260 250A
* NEC 240.4(D) Small Conductor Rule: For 14, 12, and 10 AWG copper, the Code strictly overrides the 'next size up' rule. Even if your 12 AWG wire has 90°C THHN insulation (rated 30A), the maximum breaker you can install is 20A. This is a hard safety limit to prevent small wires from overheating under high-fault currents before the breaker trips.

Which Column Applies and How Derating Modifies the Base Value

The most common mistake DIYers and apprentice electricians make is looking at the 90°C column because modern THHN/THWN-2 wire is stamped with that rating. You cannot use the 90°C column for your final ampacity unless both the wire and every single termination point are rated for 90°C. In residential and light commercial work, almost no breakers, receptacles, or switches are rated for 90°C.

The Weakest Link Rule (Termination Temperatures)

NEC 110.14(C) dictates that the ampacity of a circuit is limited by the lowest temperature rating of any connected component. Here is how to choose your column:

  • The 60°C Column: Use this if you are using NM-B (Romex) cable. NEC 334.80 explicitly limits NM-B ampacity to the 60°C column, regardless of the fact that the internal conductors might have 90°C insulation. Also use this column for older equipment or any breaker/receptacle not explicitly marked with a temperature rating.
  • The 75°C Column: Use this when pulling individual THHN/THWN-2 conductors in conduit, provided the breakers and lugs are marked 75°C (standard for almost all modern Square D, Eaton, and Siemens load centers and breakers rated 100A or less).

Applying Derating Factors (The 90°C Column's Real Purpose)

When you bundle more than three current-carrying conductors in a single raceway or conduit, they heat each other up. You must apply a derating factor from NEC Table 310.15(C)(1). This is where the 90°C column is legally useful. You perform your derating math starting from the 90°C base ampacity, but your final derated number cannot exceed the ampacity of the termination temperature column.

Worked Derating Example: You are pulling six current-carrying 12 AWG THHN wires through a single EMT conduit to feed three separate 20A circuits.

1. Base 90°C ampacity for 12 AWG = 30A.
2. Derating factor for 4-6 conductors = 80%.
3. Math: 30A × 0.80 = 24A.
4. Check termination limit: The 60°C column for 12 AWG is 20A.
5. Result: Since 24A is greater than the 20A termination limit, the wire is still legally permitted to be used on a 20A breaker. If you had 7 to 9 conductors (70% derating: 30A × 0.70 = 21A), you would still be fine. But at 10 conductors (50% derating: 30A × 0.50 = 15A), you would be forced to upsize to 10 AWG wire.

What Counts as a Current-Carrying Conductor?

Grounding wires (bare or green) and equipment grounding conductors never count toward your derating total. Neutrals are trickier: in a standard single-phase, 2-wire circuit, the neutral carries the same unbalanced current and does count. In a standard 3-phase or multi-wire branch circuit (MWBC) serving only linear loads, the neutral does not count. However, if you are feeding modern electronic loads (LED drivers, computers) that generate harmonic currents on a shared neutral, the neutral must be counted as a current-carrying conductor.

What This Chart Cannot Tell You (Voltage Drop & Ambient Limits)

The wire gauge amps chart assumes an ambient temperature of 30°C (86°F) and relatively short wire runs. If your installation deviates from these baseline conditions, the chart alone will lead you to undersize your wire.

Voltage Drop Over Distance

Ampacity measures a wire's ability to dissipate heat without melting the insulation. It does not measure the wire's ability to deliver adequate voltage to the load. NEC 310.15(B) Informational Note recommends a maximum voltage drop of 3% for branch circuits and 5% for the combined feeder and branch circuit. While not strictly enforceable as a hard code violation in all jurisdictions, failing to account for voltage drop will result in dim lights, tripping motor overloads, and shortened appliance lifespans.

For practical benchmarking on a 120V circuit (where a 3% drop equals 3.6 volts):

  • 14 AWG on a 15A load: Max recommended length is ~50 feet.
  • 12 AWG on a 20A load: Max recommended length is ~57 feet.
  • 10 AWG on a 30A load: Max recommended length is ~72 feet.

If you are wiring a detached garage or a long driveway lighting run that exceeds these distances, you must upsize the wire purely for voltage drop, even if the ampacity chart says the smaller wire can handle the thermal load. Use a dedicated voltage drop calculator from a major wire manufacturer to find the exact upsizing requirements for your specific footage and load.

Ambient Temperature Corrections

If you are routing wires through an attic in the summer, near a boiler, or in a high-temperature industrial space, the 30°C baseline no longer applies. NEC Table 310.15(B)(1) provides correction factors. For example, if your attic reaches 50°C (122°F), you must multiply the base ampacity of your THHN (90°C column) by 0.82. A 10 AWG wire that normally carries 40A at 90°C is now limited to 32.8A (40 × 0.82) before you even apply bundling derating or termination limits.

The 125% Continuous Load Rule

Finally, the chart lists raw thermal ampacity, not circuit design limits. NEC 210.20(A) requires that if a load is expected to run continuously for 3 hours or more (like an EV charger, a hardwired heater, or commercial lighting), the branch circuit must be sized at 125% of the continuous load. Therefore, a 16A continuous EV charger requires a wire and breaker sized for 20A (16 × 1.25 = 20A). You would need 12 AWG wire and a 20A breaker, even though the raw load is only 16A.