For standard residential branch circuits, the baseline rule is simple: use 14 AWG for 15A, 12 AWG for 20A, and 10 AWG for 30A. For heavy appliances and subpanel feeders, step up to 6 AWG for 50A and 3 AWG for 100A. However, picking the right wire isn't just about matching a single number; it requires understanding temperature ratings, insulation types, and bundling derations.

Below is the master reference for copper conductors, designed to give you the exact part and breaker size for your next pull.

The Master AWG Amperage Table (NEC Table 310.16)

How to read this table: This data is extracted from NFPA 70 (National Electrical Code) Table 310.16. It lists the allowable ampacities for insulated copper conductors rated up to 2000 volts. The 60°C column applies to older insulation (like TW) and, crucially, to most standard residential cables (NM-B/Romex) and breakers rated 100A or less. The 75°C column applies to THHN/THWN wire in conduit and terminations rated for 75°C (common on breakers over 100A and commercial lugs). The Max Breaker column reflects standard overcurrent protection limits, including the strict small-conductor rules of NEC 240.4(D).

AWG Size 60°C Ampacity (NM-B / TW) 75°C Ampacity (THHN / THWN) Standard Max Breaker
14 AWG 15A 20A* 15A
12 AWG 20A 25A* 20A
10 AWG 30A 35A* 30A
8 AWG 40A 50A 40A
6 AWG 55A 65A 60A
4 AWG 70A 85A 70A / 80A
3 AWG 85A 100A 100A
2 AWG 95A 115A 100A / 125A
1 AWG 110A 130A 125A
1/0 AWG 125A 150A 150A
2/0 AWG 145A 175A 175A
The NM-B (Romex) Trap: Notice the asterisks on the 75°C column for 14, 12, and 10 AWG. Even though the individual THHN wires inside NM-B cable have 90°C insulation, NEC 334.80 mandates that you must use the 60°C column for final ampacity. You cannot put 12 AWG NM-B on a 25A breaker just because the 75°C column says 25A. The breaker maxes out at 20A.

Which Temperature Column Applies to Your Install?

The most common mistake DIYers make is looking at the 90°C column (not shown above, as it's rarely used for final sizing) or the 75°C column when they should be using the 60°C column. Here is the exact decision logic for which column governs your installation:

  • Use the 60°C Column if: You are using NM-B (Romex) cable, UF-B underground cable, or if your breaker/lug termination is not explicitly stamped with a temperature rating (most residential breakers 100A and under default to 60°C terminations per NEC 110.14(C)).
  • Use the 75°C Column if: You are pulling individual THHN/THWN-2 conductors in conduit and terminating them on lugs explicitly rated for 75°C (common on subpanel lugs, large disconnects, and breakers over 100A).
  • Use the 90°C Column ONLY for: Derating calculations (explained below). You can start your derating math at the 90°C ampacity, but the final derated number cannot exceed the 60°C or 75°C ampacity limit of your terminations.

Derating: When the Base Table Lies

The amperage table AWG values above assume two things: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together. When you violate either assumption, the wire cannot dissipate heat as efficiently, and you must "derate" (reduce) its ampacity.

How derating modifies the base value: You multiply the base ampacity by a correction factor. Let's look at a real-world scenario: You are pulling four current-carrying conductors (e.g., two hots, a neutral, and a switched hot for a 3-way circuit) through a single conduit to a detached garage.

  1. Identify the bundling penalty: NEC Table 310.15(C)(1) states that 4 to 6 current-carrying conductors require an 80% derating factor.
  2. Apply to the 90°C column: 12 AWG THHN has a 90°C ampacity of 30A. Multiply 30A × 0.80 = 24A.
  3. Check the termination limit: Your breaker and receptacles are rated 60°C/75°C. The 60°C limit for 12 AWG is 20A. Since 24A is greater than 20A, your final allowable ampacity is capped at 20A.
Pro-Tip on Neutrals: In a standard single-phase, 120/240V multi-wire branch circuit (MWBC) or a standard 120V circuit, the neutral carries the unbalanced current and does count as a current-carrying conductor. However, in a pure 240V-only circuit (like a baseboard heater or water heater with no 120V tap), the white wire is just a grounded conductor carrying zero current and does not count toward your bundling deration.

Decision Tree: Pick Your Exact Wire and Breaker

Stop guessing. Use this decision-tree-table to terminate your project planning with a concrete materials list. Find your load type on the left, and buy the exact wire and breaker on the right.

If Your Load / Circuit Is... Then Use This Wire (Copper) Install This Breaker
Standard 15A lighting or bedroom receptacles 14/2 NM-B (14 AWG) 15A Standard or AFCI
Kitchen/Bathroom receptacles, garage, outdoor 12/2 NM-B (12 AWG) 20A GFCI or AFCI
Electric dryer (30A, 120/240V) 10/3 NM-B (10 AWG) 30A Double-Pole
Electric range/oven (40A-50A) 6/3 NM-B or 6 AWG THHN 50A Double-Pole
Hot tub / Spa (50A, outdoor conduit) 6 AWG THWN-2 in conduit 50A GFCI Double-Pole
100A Subpanel Feeder (up to 100ft) #3 AWG THHN or 2/0 Aluminum 100A Main Lug / Breaker
200A Service Entrance / Main Feeder 4/0 Aluminum (SER cable) 200A Main Breaker

What This Amperage Table AWG Chart Cannot Tell You

While NEC Table 310.16 is the bible for preventing wires from melting under load, it is blind to three critical physical realities. If you ignore these, your installation will fail inspection or perform poorly.

1. Voltage Drop Over Distance

Ampacity tables assume the wire can handle the heat, but they don't care if the voltage at the far end sags to 105V. For any run exceeding 100 feet, you must calculate voltage drop. A 50A hot tub 150 feet away on 6 AWG wire will experience roughly a 4.5% voltage drop under full load, which is borderline. Sizing up to 4 AWG copper for that specific run reduces the drop to a safe 2.8%. Use a dedicated voltage drop calculator for any run over 75 feet.

2. Physical Lug Constraints

The table might tell you that 4 AWG copper is rated for 85A at 75°C, meaning it's technically fine for a 70A breaker. But if you try to cram a stiff 4 AWG solid or stranded wire into the tiny lug of a standard residential 70A breaker, you will strip the lug screw or fail to get the torque wrench on it. Always check the breaker manufacturer's datasheet (Square D, Eaton, Siemens) for the maximum AWG their specific lug accepts.

3. Short-Circuit Withstand Ratings

Ampacity is about continuous thermal loading. It does not tell you if the wire can survive the magnetic and thermal shock of a dead short before the breaker trips. This is why you cannot use 18 AWG wire on a 100A breaker just because the load only draws 2 amps; the wire would vaporize before the breaker's magnetic trip mechanism could clear the fault. The overcurrent device must be sized to protect the wire's physical mass, not just the load's appetite.