If you need a direct answer for standard residential branch circuits: use 14 AWG for 15A, 12 AWG for 20A, 10 AWG for 30A, 8 AWG for 40A, and 6 AWG for 50A. However, picking the right wire gauge for a breaker isn't always that simple. The correct size depends heavily on your insulation type, termination ratings, and installation environment.

Below is the complete amp to wire chart based on the National Electrical Code (NEC) Table 310.16 for copper conductors. Bookmark this page for quick jobsite lookups.

The NEC Amp to Wire Chart (Copper Conductors)

How to read this table: This chart lists the allowable ampacities for insulated copper conductors rated up to 2000 volts. The two most critical columns are 60°C (140°F) and 75°C (167°F). You must select your column based on the temperature rating of the weakest link in your circuit—usually the breaker lugs, receptacles, or the specific cable assembly (like NM-B). Values are based on an ambient air temperature of 30°C (86°F).

Quick-Jump: Most Queried Breaker Sizes (Copper)
  • 15A Breaker: 14 AWG (Max 15A per NEC 240.4(D))
  • 20A Breaker: 12 AWG (Max 20A per NEC 240.4(D))
  • 30A Breaker: 10 AWG (Max 30A per NEC 240.4(D))
  • 40A Breaker: 8 AWG
  • 50A Breaker: 6 AWG
  • 100A Breaker: 3 AWG (at 75°C) or 1 AWG (at 60°C)
AWG / kcmil Size 60°C (140°F) Ampacity 75°C (167°F) Ampacity Common Insulation Types
14 AWG15A20A*TW, UF-B
12 AWG20A25A*TW, UF-B
10 AWG30A35A*TW, UF-B
8 AWG40A50ATHHW, THW, XHHW
6 AWG55A65ATHHW, THW, XHHW
4 AWG70A85ATHHW, THW, XHHW
3 AWG85A100ATHHW, THW, XHHW
2 AWG95A115ATHHW, THW, XHHW
1 AWG110A130ATHHW, THW, XHHW
1/0 AWG125A150ATHHW, THW, XHHW
2/0 AWG145A175ATHHW, THW, XHHW
3/0 AWG165A200ATHHW, THW, XHHW
4/0 AWG195A230ATHHW, THW, XHHW

*Note: While 14, 12, and 10 AWG wires have higher ampacities in the 75°C column, NEC 240.4(D) strictly limits their overcurrent protection (breaker size) to 15A, 20A, and 30A respectively for small conductors.

Which Column Applies to Your Installation?

The most common mistake DIYers and junior apprentices make is blindly using the 75°C or 90°C column because they bought THHN wire (which is rated for 90°C). The wire's insulation rating is only half the equation. You must follow NEC 110.14(C), which governs termination temperature limits.

The 60°C Rule for Small Circuits: For circuits rated 100 amps or less, or using wire sizes 14 AWG through 1 AWG, you must use the 60°C column unless the equipment (breaker, receptacle, lug) is explicitly listed and marked for 75°C. Modern residential breakers (like Square D QO or Eaton BR) and standard duplex receptacles are generally rated for 75°C, allowing you to use the 75°C column for 8 AWG and larger. However, if you are connecting to older equipment or specific devices marked only for 60°C, the 60°C column is legally binding.

The NM-B (Romex) Trap: Standard nonmetallic-sheathed cable (NM-B, commonly called Romex) has 90°C rated conductors inside. However, per NEC 334.80, the ampacity of NM-B cable must be determined using the 60°C column of Table 310.16, regardless of the 90°C insulation. A 10 AWG NM-B cable is legally limited to 30A, not 35A.

How Derating Modifies the Base Value: Table 310.16 assumes two ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together. If your installation deviates, you must apply derating factors.

  • Ambient Temperature: If you run wire through a hot attic that reaches 45°C (113°F), you must multiply the base ampacity by a correction factor (0.87 for 75°C wire). An 8 AWG THHN wire (50A base at 75°C) derates to 43.5A. It can still protect a 40A breaker, but it cannot protect a 45A breaker.
  • Conduit Bundling: If you pull four to six current-carrying conductors in a single conduit, you must derate the ampacity to 80% of its base value. For example, if you pull four 6 AWG THHN wires (65A base at 75°C) through a conduit, the adjusted ampacity drops to 52A (65 x 0.80). You must drop your breaker size from 60A down to 50A.

What This Amp to Wire Chart Cannot Tell You

An amp to wire chart is strictly a thermal limit guide. It tells you the maximum current a wire can carry before its insulation begins to degrade or melt. It completely ignores voltage drop, which is a function of distance and resistance.

If you use this chart to size a 50A RV outlet (using 6 AWG copper) and the outlet is located 150 feet from the panel, the wire will not overheat, but the voltage drop will be approximately 4.5%. The NEC recommends a maximum voltage drop of 3% for branch circuits to ensure equipment operates efficiently and motors don't burn out from undervoltage.

The Distance Fix: For long runs, you must upsize the wire purely to combat resistance, even if the breaker is small. You can verify your exact drop using a reliable tool like the Southwire Voltage Drop Calculator. As a rule of thumb for 120V circuits, upsize your wire by one AWG step for every 50 feet of run beyond the initial 50 feet.

Aluminum vs. Copper: This chart is exclusively for copper. If you are running a feeder to a subpanel using aluminum wire (like SER or XHHW-2 Al), aluminum has higher resistance and lower thermal mass. You must jump up two AWG sizes to achieve the same ampacity. For a 100A subpanel feeder, you cannot use 3 AWG copper equivalents; you must use 1 AWG aluminum (rated 100A at 75°C). Always verify the termination lugs on your subpanel are rated for aluminum (marked AL/CU) and apply an anti-oxidant compound like Noalox to the strands before torquing to the manufacturer's spec.

Always treat the NEC as the baseline minimum. Local Authorities Having Jurisdiction (AHJ) or specific equipment manufacturer instructions may require larger wire sizes or stricter derating practices. When in doubt, upsizing the wire by one gauge costs a few extra dollars but saves you from failed inspections and overheated terminations.