The Complete American Wire Gauge AWG Chart & Sizing Decision Guide

For standard residential copper wiring, the baseline American Wire Gauge AWG chart dictates that 14 AWG handles 15 amps, 12 AWG handles 20 amps, and 10 AWG handles 30 amps. These three sizes cover 90% of household branch circuits. However, sizing wire for subpanels, heavy appliances, or long conduit runs requires navigating the temperature columns and derating factors outlined in the National Electrical Code (NEC). This guide provides the master lookup table, explains which column applies to your specific installation, and gives you a concrete decision path to select the exact wire and breaker for your project.

The Master American Wire Gauge AWG Chart (NEC Table 310.16)

The table below is derived directly from NEC Table 310.16 for copper conductors. Before using it, understand how to read the columns: the 60°C column applies to NM-B (Romex) cable and older devices; the 75°C column applies to most modern breaker terminals and THWN wire in wet locations; the 90°C column applies to THHN wire in dry conduit, but only for calculating derating factors. Bookmark this section for quick reference on the most queried residential and light-commercial sizes.

Which Temperature Column Actually Applies to Your Install?

The most common mistake DIYers make is looking at the 90°C column for THHN wire and assuming they can use that higher ampacity for their breaker sizing. The NEC enforces a "weakest link" rule under Article 110.14(C). Your final allowable ampacity is limited by the lowest temperature rating of any component in the circuit.

• Use the 60°C Column when: You are running NM-B (Romex) cable, dealing with older homes with legacy breakers, or connecting to devices explicitly marked for 60°C. Because the jacket of NM-B cannot dissipate heat as well as individual wires in conduit, it is permanently locked to the 60°C column.
• Use the 75°C Column when: You are terminating THHN/THWN-2 wires into modern breakers, lugs, and receptacles. Almost all standard Square D, Eaton, and Siemens breakers manufactured after 1995 are rated for 75°C terminations.
• Use the 90°C Column when: You are calculating derating factors for THHN wire inside a conduit. You start your math here, but your final terminated ampacity must still respect the 75°C or 60°C limits of your endpoints.

How Derating Factors Modify Your Base Ampacity

The ampacities in the master chart assume two ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together. When reality deviates from these assumptions, you must derate the wire using the 90°C column as your baseline, referencing Southwire's official ampacity and derating tables.

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

When you pull more than three current-carrying conductors (hot and neutral wires; grounds do not count) through a single conduit, the trapped heat reduces the wire's capacity.

• 4 to 6 conductors: Multiply 90°C ampacity by 80%.
• 7 to 9 conductors: Multiply 90°C ampacity by 70%.
• 10 to 20 conductors: Multiply 90°C ampacity by 50%.

Example: You are pulling four 10 AWG THHN current-carrying conductors in a conduit for two 240V circuits. The 90°C base is 40A. Multiply 40A by 0.80 = 32A. Since 32A is still above the 30A maximum breaker limit for 10 AWG, you can safely use 30A breakers.

2. Ambient Temperature Derating (NEC Table 310.15(B)(1))

If your conduit runs through an attic that reaches 120°F (49°C) or along a hot roof deck, you must apply a temperature correction factor. For 90°C THHN wire at 120°F, the correction factor is 0.82. A 6 AWG wire (75A base) derates to 61.5A, which still safely supports a 60A breaker.

Wire Sizing Decision Tree: Pick Your Exact AWG

Use this decision matrix to terminate your sizing process with a concrete material pick. This assumes standard residential copper wire, 120V/240V single-phase power, and standard run lengths under 50 feet.

What the AWG Chart Cannot Tell You (Edge Cases)

The NEC Table 310.16 ampacity chart is strictly a thermal limit chart. It tells you the point at which the wire's insulation will melt or degrade. It does not account for electrical efficiency or physical space. Before finalizing your wire size, check these two critical constraints:

1. Voltage Drop (The 3% Rule)

A 10 AWG wire might safely carry 30A without overheating, but if you run it 150 feet to a detached garage, the resistance of the copper will cause the voltage to drop below 114V at the load. This causes motors to overheat and lights to dim. For any run exceeding 50 feet, calculate voltage drop. If the drop exceeds 3% for a branch circuit or 5% for the total feeder + branch, you must step up one AWG size (e.g., from 10 AWG to 8 AWG) purely to reduce resistance, even if the breaker size remains the same.

2. Conduit Fill Capacity (NEC Chapter 9)

You might determine that four 6 AWG THHN wires are electrically sufficient for your feeder, but physically, they might not fit inside a 3/4-inch PVC conduit. NEC Chapter 9, Table 1 limits conduit fill to 40% for three or more wires. Always cross-reference your wire count and AWG against a conduit fill calculator. If you are pulling three 4/0 AWG conductors for a 200A service, you are legally required to use a minimum of 2-inch conduit, regardless of the wire's ampacity.

By combining the thermal limits of the American Wire Gauge AWG chart with the physical constraints of voltage drop and conduit fill, you ensure an installation that is not only code-compliant and safe, but electrically efficient for the lifespan of the building.