For standard residential branch circuits, the direct answer for copper cable gauge AWG sizing is: 14 AWG is rated for 15 amps, 12 AWG for 20 amps, 10 AWG for 30 amps, and 8 AWG for 40 amps. These baseline numbers assume you are using standard NM-B (Romex) cable and sizing to the 60°C temperature column as mandated by the National Electrical Code (NEC).

However, picking the right wire gauge is rarely as simple as memorizing four numbers. The ampacity of a conductor changes based on its insulation type, the temperature rating of your breaker lugs, and how many wires are stuffed into a single conduit. This reference guide provides the exact data you need to size conductors safely and legally.

How to Read This Chart: The table below is derived directly from NEC 2023 Table 310.16 (formerly 310.15(B)(16)). It lists the allowable ampacities for insulated copper conductors rated up to 2000 volts. The columns are split by temperature rating (60°C, 75°C, and 90°C). Always cross-reference the "Max Standard Breaker" column, which applies the NEC 240.4(D) small conductor rules and standard breaker sizing limits.

The Master Cable Gauge AWG Ampacity Chart (NEC Table 310.16)

Use these quick-jump links to find the most commonly queried residential and light-commercial wire sizes:

Table 1: Copper Conductor Ampacities & Breaker Limits (Ambient Temp 30°C / 86°F)
Cable Gauge AWG 60°C (NM-B / TW) 75°C (THWN / Terminations) 90°C (THHN / Derating Base) Max Standard Breaker
14 AWG15A20A25A15A
12 AWG20A25A30A20A
10 AWG30A35A40A30A
8 AWG40A50A55A40A (or 50A)*
6 AWG55A65A75A60A
4 AWG70A85A95A80A (Next Size Up)
3 AWG85A100A110A100A
2 AWG95A115A130A125A (Next Size Up)
1 AWG110A130A145A125A
1/0 AWG125A150A170A150A
2/0 AWG145A175A195A175A
3/0 AWG165A200A225A200A
4/0 AWG195A230A260A225A

*Note: 8 AWG can be used on a 50A breaker ONLY if the wire is in conduit (THHN/THWN) and both the breaker and equipment terminations are explicitly rated for 75°C. NM-B cable is strictly limited to 40A.

Which Temperature Column Applies to Your Installation?

The most common mistake DIYers and junior electricians make is looking at the 90°C column because the wire jacket says "THHN" (which is 90°C rated) and assuming they can push more current through it. You cannot. The NEC enforces a "weakest link" rule for terminations.

The 60°C Rule for NM-B (Romex)

If you are running standard nonmetallic-sheathed cable (NM-B) through your wall studs, NEC 334.80 explicitly states that the ampacity must be determined using the 60°C column, regardless of the fact that the individual conductors inside the jacket are technically 90°C THHN. Therefore, 12 AWG NM-B is strictly limited to 20 amps.

The 75°C Rule for Conduit and Terminations

When you pull individual THHN/THWN-2 conductors through EMT or PVC conduit, you can use the 75°C column for your final ampacity—provided your breaker lugs and equipment terminations are rated for 75°C. Nearly all modern residential breakers (Square D Homeline, Siemens, Eaton BR) and standard receptacles are rated for 75°C. This is why 4 AWG copper in conduit can safely be paired with an 85A load (rounded up to a 90A breaker under the next-size-up rule), while 4 AWG NM-B is capped at 70A.

When to Use the 90°C Column

The 90°C column is almost never used to determine your final breaker size. Its primary purpose is to serve as the base starting point for derating calculations, which brings us to the next critical factor.

Derating Factors: When Your Base Ampacity Drops

The ampacity values in the chart above assume an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a raceway. When you bundle wires together, they cannot dissipate heat effectively. According to NFPA 70 (NEC) Table 310.15(C)(1), you must apply a derating multiplier to the 90°C column when you have four or more current-carrying conductors in a single conduit.

Warning: Neutral wires that carry only the unbalanced load from a standard single-phase circuit do not count as current-carrying. However, neutrals on 3-phase circuits, or neutrals feeding non-linear loads (like LED drivers or computers) that generate harmonic currents, do count and must be included in your derating math.

Derating Multipliers

  • 4 to 6 conductors: 80% of base 90°C ampacity
  • 7 to 9 conductors: 70% of base 90°C ampacity
  • 10 to 20 conductors: 50% of base 90°C ampacity

Worked Example: Sizing a Multi-Wire Conduit Run

Imagine you are pulling two 20-amp circuits (two hots, two neutrals) through a single piece of 1/2-inch EMT conduit to a garage subpanel. You have four current-carrying conductors.

  1. Start with the 90°C column for 12 AWG THHN: 30A.
  2. Apply the 80% derating factor for 4-6 conductors: 30A × 0.80 = 24A.
  3. Because the derated ampacity (24A) is still higher than the 20A breaker protecting the circuit, 12 AWG is legally compliant and safe.

If you were to add a third circuit to that same conduit (6 current-carrying conductors), you would still use the 80% multiplier, but if you added a fourth circuit (8 conductors), you would drop to the 70% multiplier. 30A × 0.70 = 21A. You are still safe on a 20A breaker, but you are getting dangerously close to the limit, and upsizing to 10 AWG would be the prudent choice to prevent voltage drop and heat buildup.

What This Cable Gauge AWG Table Cannot Tell You

While NEC Table 310.16 is the bible for thermal limits and fire prevention, it completely ignores two other critical physics realities: voltage drop and conduit fill. Relying solely on the ampacity chart can result in a system that is legally compliant but functionally useless.

Voltage Drop Limits

Ampacity tables assume the wire is short. If you are running a 12 AWG circuit 150 feet from the panel to a detached workshop and pulling 16 amps, the wire will not melt (it is safely under the 20A limit). However, you will experience a voltage drop of roughly 7.7 volts (over 6%). According to Electrical Contractor Magazine (ECMAG) and NEC Informational Note 210.19(A), branch circuit voltage drop should be kept under 3% for maximum efficiency. For long runs, you must use a voltage drop calculator and upsize your wire—often jumping from 12 AWG to 8 AWG or 6 AWG purely to maintain voltage at the receptacle.

Conduit Fill Capacity

The chart tells you how hot the wire will get, but it does not tell you if the wire will physically fit in the pipe. NEC Chapter 9, Table 1 limits conduit fill to 40% of the conduit's internal cross-sectional area when pulling three or more wires. For example, you can legally fit seventeen 12 AWG THHN wires inside a 1-inch EMT conduit based on physical space, but if you actually pull 17 current-carrying wires, NEC Table 310.15(C)(1) forces you to derate to 50%. Your 12 AWG wire (30A × 0.50) is now only good for 15 amps, requiring you to downsize your breaker. Always check both thermal derating and physical fill charts before pulling wire.

Short-Circuit Withstand Ratings

Finally, the table does not account for let-through current during a catastrophic short circuit. While a 14 AWG wire is fine for a 15A continuous load, if a dead-bolt short occurs, the magnetic trip of the breaker takes a few milliseconds to clear the fault. The wire must withstand that massive instantaneous spike without vaporizing. This is why the NEC strictly prohibits using 14 AWG wire on a 20A breaker, even if the continuous load is only 10 amps; the 20A breaker's fault-clearing threshold could allow the 14 AWG wire to catch fire before the trip mechanism engages.