If you need the quick numbers for standard residential copper wire (NM-B / Romex) protected by standard breakers, here is the direct answer: 14 AWG is 15 amps, 12 AWG is 20 amps, 10 AWG is 30 amps, 8 AWG is 40 amps, and 6 AWG is 55 amps.
However, grabbing a single number from a generic internet table is how you end up with melted lugs or a failed inspection. The definitive American wire gauge amperage chart is governed by the National Electrical Code (NEC), specifically Table 310.16 (formerly 310.15(B)(16)). This table doesn't just give you one number per wire size; it provides ampacities across three distinct temperature columns. Knowing which column to use, how to derate for bundling, and where the chart's limits end is the difference between a safe installation and a fire hazard.
How to Read the American Wire Gauge Amperage Chart
Table 310.16 is divided by conductor material (Copper vs. Aluminum) and insulation temperature rating (60°C, 75°C, and 90°C). Here is how to determine which column applies to your specific installation:
- The 60°C (140°F) Column: Per NEC 110.14(C)(1)(a), you must use this column for circuits rated 100A or less (which covers 14 AWG through 1 AWG), unless the equipment terminals are explicitly marked for 75°C. Standard residential NM-B (Romex) cable is also strictly limited to the 60°C column, regardless of the breaker terminal rating.
- The 75°C (167°F) Column: Use this for circuits over 100A (1/0 AWG and larger), or for smaller wires if both the wire insulation (like THHN) and the equipment lugs are explicitly rated for 75°C. Most modern commercial breakers and subpanel lugs carry a 75°C rating.
- The 90°C (194°F) Column: This is the most misunderstood column. You cannot use the 90°C ampacity to size your final breaker. It is used exclusively as the starting baseline for derating calculations (adjusting for ambient heat or bundling multiple wires in a conduit).
The Complete AWG Ampacity Table (Copper & Aluminum)
Below is the complete reference data extracted from NFPA 70 (NEC) Table 310.16. We have included anchor IDs for the most queried residential and light-commercial sizes so you can bookmark them for quick jobsite lookups.
| Wire Size (AWG/kcmil) | Copper 60°C | Copper 75°C | Copper 90°C | Aluminum 75°C |
|---|---|---|---|---|
| 14 AWG | 15A* | 20A* | 25A* | — |
| 12 AWG | 20A* | 25A* | 30A* | — |
| 10 AWG | 30A | 35A | 40A | — |
| 8 AWG | 40A | 50A | 55A | 40A |
| 6 AWG | 55A | 65A | 75A | 50A |
| 4 AWG | 70A | 85A | 95A | 65A |
| 3 AWG | 85A | 100A | 115A | 75A |
| 2 AWG | 95A | 115A | 130A | 90A |
| 1 AWG | 110A | 130A | 145A | 100A |
| 1/0 AWG | 125A | 150A | 170A | 120A |
| 2/0 AWG | 145A | 175A | 195A | 135A |
| 3/0 AWG | 165A | 200A | 225A | 155A |
| 4/0 AWG | 195A | 230A | 260A | 180A |
* Note on 14, 12, and 10 AWG: NEC 240.4(D) mandates strict overcurrent device limits for small conductors. Regardless of the 75°C or 90°C column values, 14 AWG copper is capped at a 15A breaker, 12 AWG at 20A, and 10 AWG at 30A for standard residential branch circuits.
Derating and Edge Cases: What the Chart Cannot Tell You
The ampacity table assumes a baseline ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a single raceway. When real-world conditions change, you must apply derating factors. This is where the 90°C column earns its keep.
How Derating Rows Modify the Base Value
Imagine you are pulling four current-carrying 10 AWG THHN conductors through a single conduit to feed a 240V subpanel. Table 310.16 lists 10 AWG THHN at 40A in the 90°C column. Because you have four conductors bundled, NEC Table 310.15(C)(1) requires an 80% derating multiplier.
The Math: 40A × 0.80 = 32A.
However, because your breaker and panel lugs are likely rated for 75°C (or 60°C for smaller gear), you cannot terminate a wire carrying 32A on a 30A-rated lug. The wire's insulation is thermally fine, but the termination isn't. You must step up to 8 AWG wire to maintain code compliance. For a deeper look into termination rules, Electrical Technology's AWG guide provides excellent visual breakdowns of these thermal limits.
What the Table Cannot Tell You
Relying solely on Table 310.16 leaves three critical blind spots in your design:
- Voltage Drop: The NEC table only addresses thermal limits (preventing the wire from melting). It does not guarantee your equipment will get adequate voltage. For long runs (typically over 100 feet), you must calculate voltage drop using Chapter 9, Table 8 (conductor resistance). A 3% drop is the standard target for branch circuits.
- Conduit Fill: You might thermally derate four 6 AWG wires in a 3/4-inch conduit, but physically, they might not fit. Chapter 9, Table 1 dictates maximum conduit fill percentages (40% for three or more wires) to prevent jamming and insulation damage during the pull.
- Short-Circuit Let-Through Current: Ampacity charts assume standard overcurrent protection. They do not account for the magnetic forces and thermal stress of a massive short-circuit fault, which requires checking the interrupting rating (AIC) of your breakers and the bracing of your busbars.
Frequently Asked Questions
What size wire do I need for a 50-amp breaker?
For a standard 50A circuit (like an electric range or EV charger), you need 6 AWG copper if your equipment terminals are rated for 75°C, or 4 AWG copper if they are limited to 60°C. If you are using aluminum wire (like SER cable for a feeder), you must step up to 4 AWG aluminum (rated 65A at 75°C) because aluminum has higher resistance and lower ampacity per size.
Can I use the 90°C column to size my breaker for higher amperage?
No. This is a common DIY mistake. Even if you use 90°C rated THHN wire, the breakers, lugs, and splices in standard residential panels are almost universally rated for 75°C or 60°C. The weakest link in the thermal chain dictates the maximum ampacity. You can only use the 90°C column as a starting point before applying derating multipliers for heat or bundling.
Why does my 8 AWG wire only allow 40 amps when the chart says 50 amps?
If you are using NM-B (Romex) cable, NEC 334.80 strictly limits the ampacity to the 60°C column, regardless of the breaker's terminal rating. In the 60°C column, 8 AWG copper is capped at 40A. To get the full 50A out of 8 AWG copper, you must pull individual THHN/THWN wires in conduit and terminate them on 75°C rated lugs.
Does the ground wire count towards conduit fill and derating?
For ampacity derating (the 80% bundling multiplier), an equipment grounding conductor does not count as a current-carrying conductor under normal operation, so you exclude it from the count. However, for physical conduit fill calculations (ensuring the wires actually fit inside the pipe), the ground wire does count and takes up physical cross-sectional area.
