For standard residential copper wiring, the baseline ampacities are: 14 AWG = 15A, 12 AWG = 20A, 10 AWG = 30A, 8 AWG = 40A, and 6 AWG = 55A. These baseline numbers come directly from the National Electrical Code (NEC) Table 310.16. However, picking the right wire isn't just about matching the breaker size to the smallest gauge that fits; you must account for insulation temperature ratings, ambient heat, and conductor bundling. Below is the complete reference chart, the rules for reading it, and a decision tree to lock in your exact wire size.

The Master AWG Wire Amp Chart (NEC Table 310.16)

This table is derived from NFPA 70 (NEC) Table 310.16 for copper conductors. Before reading the rows, understand the columns: the temperature ratings (60°C, 75°C, 90°C) refer to the insulation type and the termination temperature rating of your breakers and lugs, not the ambient room temperature. Bookmark this section for quick lookups on the most common residential branch circuit and feeder sizes.

AWG Size 60°C Column (TW, UF-B) 75°C Column (THWN, RHW) 90°C Column (THHN, XHHW-2)
14 AWG15A20A25A
12 AWG20A25A30A
10 AWG30A35A40A
8 AWG40A50A55A
6 AWG55A65A75A
4 AWG70A85A95A
3 AWG85A100A115A
2 AWG95A115A130A
1 AWG110A130A145A
1/0 AWG125A150A170A
2/0 AWG145A175A195A
3/0 AWG165A200A225A
4/0 AWG195A230A260A
Critical Code Caveat (NEC 240.4(D)): You might look at the 90°C column and assume 14 AWG THHN can be put on a 25A breaker. It cannot. NEC 240.4(D) strictly limits small conductors: 14 AWG is capped at 15A, 12 AWG at 20A, and 10 AWG at 30A for overcurrent protection, regardless of how high their 90°C insulation rating goes.

Which Temperature Column Applies to Your Installation?

The most common mistake DIYers make is using the 90°C column to size their breaker. The NEC requires you to use the lowest temperature rating in the entire circuit path. Here is how to determine which column dictates your final breaker size:

  • The 60°C Column: Use this for Non-Metallic Sheathed Cable (NM-B, commonly called Romex) and Underground Feeder (UF-B) cable. You must also use this column if your circuit breaker is rated for 100A or less and the manufacturer does not explicitly mark the termination lugs as 75°C. Most standard residential branch circuits fall here.
  • The 75°C Column: Use this for individual THWN conductors pulled through conduit, provided your breakers and lugs are explicitly rated for 75°C (standard for breakers 100A and larger, and many modern smaller breakers from brands like Square D and Eaton).
  • The 90°C Column: This column is almost never used for final breaker sizing. Its primary purpose is to serve as the starting baseline for derating calculations (explained below) when using THHN or XHHW-2 wire.

How Derating Modifies Your Base Ampacity

Ampacity is not a fixed number; it degrades when heat cannot escape the wire. Derating forces you to reduce the allowable current based on two main factors: ambient temperature and conductor bundling. Derating calculations always start from the 90°C column for THHN/XHHW-2 wire, even if your final termination requires the 60°C column.

Bundling Derating (NEC 310.15(C)(1)): If you pull more than three current-carrying conductors (CCCs) in a single raceway or conduit, the wires heat each other up. You must multiply the 90°C ampacity by a correction factor.

  • 4 to 6 CCCs: Multiply by 80%
  • 7 to 9 CCCs: Multiply by 70%
  • 10 to 20 CCCs: Multiply by 50%
Worked Example: You are pulling four 12 AWG THHN wires through a conduit (two hots, one neutral, one ground). The ground does not count as a CCC. You have 3 CCCs. No bundling derating applies. However, if you add a second circuit (adding two more hots and a neutral), you now have 6 CCCs. You must take the 12 AWG 90°C rating (30A) and multiply by 80%, yielding 24A. Because 24A is still higher than the 60°C termination limit (20A), you can still use a 20A breaker. But if you bundled 10 CCCs, the 12 AWG drops to 15A (30A x 50%), forcing you to upsize to 10 AWG wire.

Decision Tree: Picking Your Exact Wire Size

Use this decision matrix to terminate your planning phase and pick a concrete wire size and breaker combination. Do not guess; follow the path that matches your physical installation.

Installation Scenario Required Action Concrete Pick (Wire & Breaker)
Standard 120V/240V wall outlets or lighting inside drywall using NM-B (Romex). Use 60°C column. Obey 240.4(D) limits. 14 AWG on 15A breaker (lights) OR 12 AWG on 20A breaker (receptacles).
30A dryer or RV outlet using NM-B or UF-B cable. Use 60°C column. 10 AWG is rated 30A. 10 AWG NM-B on a 30A breaker.
50A hot tub or range circuit pulled as individual wires in PVC conduit. Use 75°C column (assuming 75°C rated lugs). 6 AWG is rated 65A. 6 AWG THWN on a 50A breaker.
100A subpanel feeder pulled in conduit (4 wires: 2 hots, 1 neutral, 1 ground). 3 CCCs. Use 75°C column for terminations. 3 AWG is 100A. 3 AWG THHN/THWN on a 100A breaker.
100A subpanel feeder in conduit, but running through a 110°F attic space. Ambient temp derating applies. Start at 90°C column, apply temp correction, then verify against 75°C termination limit. 2 AWG THHN (derates safely to handle the heat while satisfying the 75°C lug requirement).

What This Chart Cannot Tell You (The Blind Spots)

While the Copper Development Association and the NEC provide the thermal limits for wire, ampacity charts completely ignore three critical physical realities of your installation:

  1. Voltage Drop: The NEC table assumes the wire is short enough that voltage drop is negligible. If you are running a 120V circuit to a detached garage 150 feet away, a 12 AWG wire on a 20A breaker will suffer a voltage drop exceeding the recommended 3% threshold. For long runs, you must upsize the wire (e.g., jumping from 12 AWG to 8 AWG) purely to maintain voltage, even if the breaker size remains 20A.
  2. Physical Lug Fit: You cannot physically terminate a 4/0 AWG wire under the lug of a standard 100A residential breaker. The mechanical design of the lug simply will not accept a conductor that thick. If your calculation demands 4/0 AWG for a 100A feeder due to extreme voltage drop or derating, you must use a lug reducer or a Polaris connector to step down to a smaller pigtail that fits the breaker.
  3. Local AHJ Amendments: The NEC is a model code. Your local Authority Having Jurisdiction (AHJ) or city inspector may have local amendments that override these tables. Some municipalities mandate 12 AWG as the absolute minimum for all branch circuits, effectively banning 14 AWG entirely. Always verify local amendments before pulling wire.

When in doubt, the hierarchy of wire sizing is: calculate for ampacity using the correct temperature column, apply derating factors, check for voltage drop, and finally, verify physical fit at the terminations. If the math yields a fractional result or lands exactly on a non-standard breaker size, always round up to the next standard breaker size (per NEC 240.4(B)), provided the wire ampacity is not artificially capped by the small conductor rules.