For standard residential branch circuits, the baseline copper wire sizing is straightforward: 14 AWG is rated for 15 amps, 12 AWG for 20 amps, and 10 AWG for 30 amps. However, as soon as you move past basic receptacles into heavy appliances, subpanels, or long conduit runs, you need to reference the exact ampacity tables and apply the correct temperature and derating multipliers. This guide provides the complete copper wire sizing chart based on the National Electrical Code (NEC) Table 310.16, along with the jobsite rules for applying it correctly.
How to Read This Copper Wire Sizing Chart
The chart below is derived directly from NEC Table 310.16, which dictates the allowable ampacities for insulated copper conductors rated up to 2000 volts. To use this table correctly, you must understand the three temperature columns and know which one applies to your specific installation.
Most modern residential breakers, lugs, and receptacles are rated for 75°C. However, NEC 240.4(D) strictly limits overcurrent protection for small conductors (14, 12, and 10 AWG) to the 60°C column, regardless of the wire's insulation rating. Furthermore, if you are using NM-B cable (commonly known as Romex), NEC 334.80 mandates that you must use the 60°C column for final ampacity, even though the individual THHN wires inside the jacket are rated for 90°C. You only use the 75°C or 90°C columns for THHN/THWN-2 wires pulled in conduit, provided the terminating equipment is explicitly rated for those higher temperatures.
Bookmark-Friendly Quick Jumps: The most frequently queried rows in the table below are tagged with anchor IDs. Jump directly to 14 AWG, 12 AWG, 10 AWG, 6 AWG, 4 AWG, or 2 AWG.
Complete Copper Wire Sizing Chart (NEC Table 310.16)
The following data assumes copper conductors, an ambient temperature of 30°C (86°F), and no more than three current-carrying conductors in a raceway or cable. Source standard: NFPA 70 (NEC) Table 310.16. For comprehensive manufacturer data, refer to the Cerrowire Ampacity Tables.
| AWG / kcmil Size | 60°C (140°F) Ampacity | 75°C (167°F) Ampacity | 90°C (194°F) Ampacity | Max Standard Breaker (OCPD) |
|---|---|---|---|---|
| 14 AWG | 15 A | 20 A | 25 A | 15 A |
| 12 AWG | 20 A | 25 A | 30 A | 20 A |
| 10 AWG | 30 A | 35 A | 40 A | 30 A |
| 8 AWG | 40 A | 50 A | 55 A | 40 A / 50 A* |
| 6 AWG | 55 A | 65 A | 75 A | 60 A |
| 4 AWG | 70 A | 85 A | 95 A | 80 A / 90 A* |
| 3 AWG | 85 A | 100 A | 115 A | 100 A |
| 2 AWG | 95 A | 115 A | 130 A | 110 A / 125 A* |
| 1 AWG | 110 A | 130 A | 145 A | 125 A / 150 A* |
| 1/0 AWG | 125 A | 150 A | 170 A | 150 A |
| 2/0 AWG | 145 A | 175 A | 195 A | 175 A |
| 3/0 AWG | 165 A | 200 A | 225 A | 200 A |
| 4/0 AWG | 195 A | 230 A | 260 A | 225 A / 250 A* |
*Note: Breaker sizes marked with an asterisk indicate scenarios where the calculated ampacity falls between standard overcurrent protective device (OCPD) sizes. NEC 240.4(B) allows you to round up to the next standard breaker size (e.g., 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250) provided the conductors are not part of a multi-outlet branch circuit supplying receptacles.
Derating and Edge Cases: What the Base Table Cannot Tell You
The base ampacities in the chart above assume ideal conditions. In the real world, you must apply derating factors that modify the base value, and you must account for limitations that the table simply does not cover.
How Derating Rows Modify the Base Value
NEC 310.15(C)(1) requires you to reduce the allowable ampacity when you bundle more than three current-carrying conductors in a single conduit or raceway. The heat generated by adjacent wires cannot dissipate, which degrades the insulation over time.
- 4 to 6 conductors: Multiply the base 90°C ampacity by 80%.
- 7 to 9 conductors: Multiply the base 90°C ampacity by 70%.
- 10 to 20 conductors: Multiply the base 90°C ampacity by 50%.
Worked Example: You are pulling four 12 AWG THHN circuits (8 current-carrying conductors) through a single 1-inch EMT conduit. The base 90°C ampacity for 12 AWG is 30A. Applying the 70% derating factor for 7-9 conductors yields 21A (30A x 0.70). Because 21A is greater than the 20A breaker requirement, 12 AWG is still legally acceptable. However, if you added a fifth circuit (10 conductors), the 50% derating factor would drop the ampacity to 15A, forcing you to upsize to 10 AWG wire to maintain a 20A circuit.
What the Table Cannot Tell You
The copper wire sizing chart is strictly a thermal limit chart. It cannot tell you about voltage drop over distance. A 10 AWG copper wire is perfectly legal on a 30A breaker for a 20-foot run to a window AC unit. But if that same unit is 150 feet away, the resistance of the 10 AWG wire will cause the voltage at the receptacle to drop below 114V under full load, potentially damaging the compressor motor. For long runs, you must calculate voltage drop (aiming for less than 3% on branch circuits) and upsize the wire accordingly, even if the breaker size remains the same.
Frequently Asked Questions
What size copper wire do I need for a 50 amp breaker?
For a standard 50-amp circuit (like an electric range or a Level 2 EV charger), you need 6 AWG copper wire if your terminating equipment is rated for 75°C, which provides 65A of base ampacity. If the equipment terminals are only rated for 60°C, or if you are using NM-B (Romex) cable, you must use the 60°C column, which limits 6 AWG to 55A. In that 60°C scenario, you must upsize to 4 AWG copper (rated 70A at 60°C) to safely and legally protect the circuit with a 50A breaker. Always check the manufacturer's installation manual for the specific appliance to verify terminal temperature ratings.
Can I use the 90°C column to size my breakers?
No, almost never. The 90°C column in the copper wire sizing chart is primarily used as the starting point for derating calculations (like the conduit bundling example above) and for specific high-temperature industrial applications. The final ampacity of your circuit is always capped by the lowest temperature rating of any component in the system. Since almost all residential breakers, panel lugs, and receptacles are rated for 75°C maximum, your final wire size must be validated against the 75°C or 60°C column, regardless of the fact that modern THHN-2 wire insulation can physically withstand 90°C.
Does this copper wire sizing chart apply to aluminum wire?
No. Aluminum has a higher electrical resistance than copper, meaning it generates more heat at the same amperage. You cannot use this copper chart for aluminum conductors. For example, while 3 AWG copper is sufficient for a 100-amp subpanel feeder, you must use 1/0 AWG aluminum to achieve the same 100-amp rating at 75°C. If you are sizing aluminum wire, you must consult NEC Table 310.16 specifically under the aluminum columns, and you must apply an antioxidant compound to the terminations to prevent galvanic corrosion and high-resistance connections over time.
