For standard residential branch circuits, the AWG wire sizes chart dictates that 14 AWG copper handles 15 amps, 12 AWG handles 20 amps, and 10 AWG handles 30 amps. These baseline numbers assume a 60°C temperature rating, an ambient temperature of 30°C (86°F), and no more than three current-carrying conductors in a raceway. However, simply memorizing three numbers will lead to failed inspections or melted insulation when you move into subpanels, feeders, or commercial work. To size wire correctly, you must understand how to read the full National Electrical Code (NEC) ampacity tables and apply the necessary derating factors.
How to Read the AWG Wire Sizes Chart
The ampacity table is not a single list of numbers; it is a matrix of temperature columns. The insulation around your wire (like THHN or XHHW) is rated for high heat—often 90°C—but the terminals on your breakers, receptacles, and switches are usually rated for lower temperatures.
Which column applies to your installation? The NEC enforces a 'weakest link' rule under Article 110.14(C). You must use the temperature column that matches the lowest-rated component in the circuit. Most modern residential breakers and receptacles are rated for 75°C, meaning you can use the 75°C column for wire sizing on circuits larger than 100 amps. However, for circuits rated 100 amps or less, or for 14, 12, and 10 AWG wire specifically, NEC 240.4(D) strictly limits you to the 60°C column for overcurrent protection, regardless of how heat-resistant your wire insulation actually is.
The Complete NEC 310.16 AWG Wire Sizes Chart
The data below is sourced directly from NFPA 70 (National Electrical Code) Table 310.16. It assumes copper and aluminum conductors in a standard raceway or cable, with an ambient temperature of 30°C (86°F) and a maximum of three current-carrying conductors.
Quick-Jump Bookmarks: 14 AWG | 12 AWG | 10 AWG | 8 AWG | 6 AWG | 4 AWG | 2 AWG
| AWG Size | Copper 60°C | Copper 75°C | Copper 90°C | Aluminum 60°C | Aluminum 75°C | Aluminum 90°C |
|---|---|---|---|---|---|---|
| 14 | 15A | 20A | 25A | -- | -- | -- |
| 12 | 20A | 25A | 30A | 15A | 20A | 25A |
| 10 | 30A | 35A | 40A | 25A | 30A | 35A |
| 8 | 40A | 50A | 55A | 30A | 40A | 45A |
| 6 | 55A | 65A | 75A | 40A | 50A | 60A |
| 4 | 70A | 85A | 95A | 55A | 65A | 75A |
| 3 | 85A | 100A | 110A | 65A | 75A | 85A |
| 2 | 95A | 115A | 130A | 75A | 90A | 100A |
| 1 | 110A | 130A | 150A | 85A | 100A | 115A |
| 1/0 | 125A | 150A | 170A | 100A | 120A | 135A |
| 2/0 | 145A | 175A | 195A | 115A | 135A | 150A |
| 3/0 | 165A | 200A | 225A | 130A | 155A | 175A |
| 4/0 | 195A | 230A | 260A | 150A | 180A | 205A |
Derating and What the Table Cannot Tell You
The chart above represents ideal, baseline conditions. On a real jobsite, you must apply derating factors that modify these base values before you select your breaker.
How derating rows modify the base value: Derating happens in two main ways: ambient temperature and conductor bundling. If your conduit runs through a 110°F attic, you must multiply the 90°C column ampacity by a correction factor (0.87 for THHN). If you pull four to six current-carrying conductors through that same conduit, you multiply by an 80% adjustment factor.
Example: You have four 12 AWG THHN copper wires in a conduit in a 90°F attic. The 90°C base is 30A. The temperature correction is 0.96, and the bundling adjustment is 0.80. Your derated ampacity is 30A × 0.96 × 0.80 = 23A. Because 23A is still above the 20A limit for 12 AWG under the 60°C rule, you can safely use a 20A breaker. If you added a fifth wire, the math would drop you below 20A, forcing an upsize to 10 AWG.
What the table cannot tell you: The ampacity chart is entirely blind to voltage drop. A 10 AWG wire is legally allowed to carry 30 amps over a 500-foot run according to the thermal limits in Table 310.16. However, at 30 amps over 500 feet, a 120V circuit will experience a massive 18% voltage drop, starving your equipment and potentially damaging motors. For long runs, you must upsize the wire strictly to maintain voltage (keeping drop under 3% for branch circuits and 5% total), entirely ignoring the thermal ampacity chart. Furthermore, the table cannot tell you if a wire will physically fit into a breaker lug; trying to cram two 4 AWG conductors into a single 100A breaker lug designed for one wire will result in a loose connection and a fire hazard.
AWG Wire Sizes Chart FAQ
What size wire do I need for a 50-amp circuit?
For a standard 50-amp circuit (like an EV charger or subpanel feeder), you need 6 AWG copper or 4 AWG aluminum. This assumes you are using the 75°C column, which applies to nearly all modern 50-amp breakers and terminals. If your run exceeds 100 feet, you must upsize to 4 AWG copper or 2 AWG aluminum to compensate for voltage drop.
Can I use 12 AWG wire on a 15-amp breaker?
Yes, it is perfectly safe and code-compliant to use a larger wire than the minimum required. 12 AWG wire on a 15-amp breaker simply means the wire will run cooler and experience less voltage drop. The only downsides are the higher material cost, the thicker wire taking up more box fill volume, and the physical difficulty of bending 12 AWG in crowded junction boxes or pushing it into the backstab holes of cheap 15A receptacles (always use the screw terminals or pigtails instead).
Why does my 10 AWG THHN wire say 90°C / 40A but I can only use it for 30A?
This is due to NEC Article 240.4(D), often called the 'small conductor rule.' To prevent hobbyists and builders from overloading small wires that are easily damaged by high-fault currents, the NEC strictly caps the overcurrent protection for 14 AWG at 15A, 12 AWG at 20A, and 10 AWG at 30A. Even if your THHN insulation is rated for 40A at 90°C, the breaker protecting a 10 AWG branch circuit cannot exceed 30 amps.
How does voltage drop change the AWG wire size I need?
Voltage drop is a function of wire length, material resistivity, and the actual current drawn, not just the breaker size. The standard AWG ampacity chart only addresses thermal limits (preventing the wire from melting). If you are running a 20-amp circuit to a detached garage 150 feet away, 12 AWG wire will drop roughly 5.5% of the voltage. To keep the drop under the recommended 3% threshold for branch circuits, the chart is useless; you must use a voltage drop calculator and upsize to 8 AWG or 6 AWG copper to ensure your tools and appliances receive adequate voltage.
