The definitive copper wire sizes chart for US residential and commercial wiring is governed by NEC Table 310.16. For standard home branch circuits, the baseline rules are simple: 14 AWG handles 15 amps, 12 AWG handles 20 amps, and 10 AWG handles 30 amps. However, pulling the correct wire requires understanding temperature columns, bundling derating, and the specific NEC rules that dictate maximum breaker sizes.

The Standard Copper Wire Sizes Chart (NEC Table 310.16)

Before referencing the table below, you must know how to read the temperature columns. Wire insulation (like THHN or XHHW) is often rated for 90°C, but your breakers and terminal lugs are typically rated for 75°C. Under NEC 110.14(C), for circuits rated 100 amps or less (which covers almost all residential branch circuits), you must use the 60°C column to determine ampacity, unless the equipment is explicitly marked for 75°C terminations. The 75°C column is generally reserved for feeders and service entrance conductors over 100A.

Bookmark Quick-Jump Rows: The most queried sizes for DIY and residential work are 14 AWG (lighting), 12 AWG (standard receptacles), 10 AWG (dryers/water heaters), 6 AWG (EV chargers/ranges), and 2 AWG (100A subpanel feeders).
Source: NEC Table 310.16 & NEC 240.4 (Copper Conductors, up to 3 current-carrying, 30°C ambient)
Wire Size (AWG/kcmil) 60°C Ampacity (Branch Circuits ≤100A) 75°C Ampacity (Feeders & Terminals) Max Standard Breaker Size
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
3 AWG 85A 100A 90A **
2 AWG 95A 115A 100A **

* NEC 240.4(D) Small Conductor Rule: Even if your 12 AWG wire has a 75°C ampacity of 25A, the NEC strictly forbids placing it on a 25A breaker. Small conductors (14, 12, and 10 AWG) are hard-capped at 15A, 20A, and 30A respectively to prevent overcurrent fires.
** NEC 240.4(B) Next Size Up Rule: Standard breakers do not come in 55A or 95A. If your calculated ampacity does not match a standard breaker size (found in NEC 240.6), you are permitted to round up to the next standard size (e.g., 55A wire gets a 60A breaker; 95A wire gets a 100A breaker), provided the load is not a continuous motor or specialized circuit.

Applying Derating Factors to Your Base Ampacity

The ampacities listed in the copper wire sizes chart above assume two ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together in a raceway or conduit. When real-world jobsite conditions deviate from this, you must apply derating factors. Derating reduces the base ampacity to account for trapped heat.

1. Bundling Derating (NEC 310.15(C)(1))

When you pull multiple circuits through a single conduit, the wires heat each other up. If you have 4 to 6 current-carrying conductors in a conduit, you must multiply the base ampacity by 80%. If you have 7 to 9 conductors, you multiply by 70%.

  • Example: You are pulling four 12 AWG THHN wires (two hots, two neutrals for two separate 120V circuits) through a single EMT conduit. The 75°C base ampacity for 12 AWG THHN is 25A. Multiply 25A by 0.80 = 20A. Your derated ampacity is exactly 20A, meaning you can still safely use a 20A breaker.
  • Gotcha: If you added two more wires (6 total), the derating drops to 80% (still 20A). But if you added eight wires total, the 70% derating drops the ampacity to 17.5A. You would then be forced to downsize your breaker to 15A or pull a second conduit.

2. Ambient Temperature Derating (NEC 310.15(B)(2))

If you are running wires through an unconditioned attic in the middle of summer, the ambient temperature can easily exceed 120°F (49°C). According to the Cerrowire Building Wire Ampacity Chart and NEC temperature correction tables, a 75°C rated wire at 46°C–50°C ambient must be derated to 82% of its base value.

Safety Note: The equipment grounding conductor (bare copper or green) and a purely neutral conductor in a standard single-phase 120V/240V residential circuit do not count as current-carrying conductors for bundling derating purposes. However, the neutral does count if you are wiring a 3-phase system or feeding non-linear loads (like heavy LED drivers or IT equipment) where harmonic currents are present.

What This Chart Cannot Tell You (And When to Size Up)

An ampacity chart is strictly a thermal limit guide. It tells you the maximum current a wire can carry before its insulation begins to melt or degrade. It does not account for electrical efficiency, physical installation constraints, or material differences.

Voltage Drop is the Hidden Limit

If you run a 12 AWG copper wire 150 feet to a shed and pull a full 20 amps, the wire will not melt (it is within thermal ampacity limits). However, the resistance of 150 feet of 12 AWG wire will cause a voltage drop of roughly 10 volts. Your 120V tools will only see 110V, which can burn out motors in compressors and table saws. The NEC recommends keeping voltage drop under 3% for branch circuits and 5% overall. For any run exceeding 50 feet at full load, ignore the minimum chart requirements and size up one AWG (use 10 AWG for a 20A circuit) purely to mitigate voltage drop.

Aluminum vs. Copper Equivalencies

This chart applies exclusively to copper. If you are pricing out a 100-amp subpanel feeder and decide to use SER (Service Entrance Rated) aluminum cable to save money, you cannot use this chart. Aluminum has higher resistance and expands/contracts more under heat. As a general rule of thumb for residential feeders, aluminum requires jumping up two AWG sizes compared to copper. To achieve the 100A capacity of 2 AWG copper, you must use 1/0 AWG aluminum.

Local AHJ Overrides

While NEC Table 310.16 is the national baseline, your local Authority Having Jurisdiction (AHJ) or municipal inspector has the final say. Some municipalities have local amendments that ban the 'next size up' rule entirely, requiring exact breaker-to-ampacity matches, or they may mandate 75°C columns for all residential work regardless of the 100A threshold. Always verify local amendments before purchasing bulk wire spools.