If you are sizing a circuit, the master reference you need is the electrical wire gauge table published in the National Electrical Code (NEC), specifically Table 310.16. For standard residential copper wire, the baseline rules are simple: 14 AWG is rated for 15 amps, 12 AWG for 20 amps, and 10 AWG for 30 amps. However, once you move into feeder circuits, conduit bundling, or high-temperature environments, reading the table correctly becomes the difference between a safe installation and a melted termination lug.
This guide provides the complete copper ampacity chart, explains exactly which temperature column applies to your specific installation, and gives you a concrete decision tree to pick your wire without guessing.
How to Read the NEC Electrical Wire Gauge Table
The most common mistake DIYers and junior apprentices make is looking at the highest number in the table and using it to size their breaker. The NEC table provides ampacities across three temperature columns: 60°C, 75°C, and 90°C. Here is how to read them:
- The 60°C Column: Use this for older installations, specific appliance cords, or when the termination temperature of your breaker or device is completely unknown. It is the most conservative rating.
- The 75°C Column: This is your default for terminations. Almost all modern breakers, lugs, and receptacles are rated for 75°C. You cannot terminate a wire on a 50A breaker if the wire's 75°C ampacity is only 40A, even if the wire's insulation is rated for 90°C.
- The 90°C Column: This column is almost exclusively used for derating calculations (adjusting for heat buildup in conduit) and ambient temperature corrections. You can use the 90°C ampacity as your starting point for derating math, but your final calculated ampacity cannot exceed the 75°C termination limit.
Complete Copper Ampacity Chart (NEC Table 310.16)
The table below covers the most queried residential and light commercial copper wire sizes. Source: NFPA 70 (National Electrical Code), Table 310.16, based on an ambient temperature of 30°C (86°F).
Quick-Jump Bookmarks: 14 AWG | 12 AWG | 10 AWG | 6 AWG | 3 AWG | 2 AWG | 4/0 AWG
| Wire Size (AWG/kcmil) | 60°C (140°F) NM-B / Romex |
75°C (167°F) Terminations |
90°C (194°F) THHN / Derating |
|---|---|---|---|
| 14 AWG | 15A | 20A* | 25A* |
| 12 AWG | 20A | 25A* | 30A* |
| 10 AWG | 30A | 35A* | 40A* |
| 8 AWG | 40A | 50A | 55A |
| 6 AWG | 55A | 65A | 75A |
| 4 AWG | 70A | 85A | 95A |
| 3 AWG | 85A | 100A | 110A |
| 2 AWG | 95A | 115A | 130A |
| 1 AWG | 110A | 130A | 145A |
| 1/0 AWG | 125A | 150A | 170A |
| 2/0 AWG | 145A | 175A | 195A |
| 3/0 AWG | 165A | 200A | 225A |
| 4/0 AWG | 195A | 230A | 260A |
* Asterisk denotes sizes restricted by NEC 240.4(D) for standard branch circuit overcurrent protection.
Derating: When the Base Table Fails You
The electrical wire gauge table above assumes you have no more than three current-carrying conductors in a raceway and an ambient temperature of 86°F (30°C). If you violate either assumption, the base ampacity drops. This is where the 90°C column saves your installation.
How derating modifies the base value:
Suppose you are pulling two 120V circuits (Hot, Hot, Neutral, Neutral = 4 current-carrying conductors) through a single PVC conduit. According to NEC Table 310.15(C)(1), 4 to 6 conductors require an 80% adjustment factor.
- Start at the 90°C column: 10 AWG THHN is rated for 40A.
- Apply the derating factor: 40A × 0.80 = 32A.
- Check the termination limit: Your breaker lugs are rated 75°C. The 75°C limit for 10 AWG is 35A. Since your derated value (32A) is below the termination limit (35A), the wire is valid.
- Final Breaker Size: You can still use a standard 30A breaker, because the derated ampacity (32A) exceeds the breaker trip rating.
If you had tried to pull 12 AWG THHN (90°C rating: 30A) for those same two circuits, the math would be: 30A × 0.80 = 24A. You could no longer use a 20A breaker for a continuous load, forcing you to upsize to 10 AWG wire.
Decision Tree: Sizing Your Circuit Wire
Stop guessing and follow this decision path to arrive at a concrete wire pick for your project. This assumes standard copper wire in a residential setting.
| If Your Application Is... | And the Run is Under 50 Feet... | And the Run is Over 100 Feet... | Concrete Pick (Buy This) |
|---|---|---|---|
| Standard 15A Lighting/Receptacle Branch | N/A | N/A | 14/2 or 12/2 NM-B (12 AWG preferred to minimize voltage drop on long daisy chains) |
| Standard 20A Kitchen/Bath Branch | N/A | N/A | 12/2 NM-B |
| 30A Dryer or RV Receptacle (120/240V) | N/A | N/A | 10/3 NM-B (or three 10 AWG THHN in conduit) |
| 50A Range or Hot Tub (120/240V) | Under 50 ft | Over 100 ft | 6/3 NM-B (Short) or 4 AWG THHN in PVC (Long) |
| 60A EV Charger Hardwire | Under 50 ft | Over 100 ft | 4 AWG THHN (Short) or 3 AWG THHN (Long) |
| 100A Subpanel Feeder (120/240V) | Under 50 ft | Over 100 ft | 3 AWG THHN in conduit (Short) or 1/0 AWG THHN (Long) |
| 200A Main Service Entrance | N/A | N/A | 2/0 AWG Copper SER (or 4/0 Aluminum SER to save cost) |
What the Ampacity Table Cannot Tell You
The NEC electrical wire gauge table is strictly a thermal limit chart. It tells you the maximum current the wire can carry before the insulation melts or degrades. It completely ignores voltage drop.
If you are wiring a detached garage subpanel 150 feet away from your main panel, Table 310.16 says 3 AWG copper is perfectly safe to carry 100A without catching fire. However, pushing 100A through 150 feet of 3 AWG copper will result in a voltage drop of roughly 6.5 volts (over 5%). Your 240V tools will see 233V, motors will run hot, and electronics may brown out.
For any run over 100 feet, you must calculate voltage drop. The industry standard rule of thumb is to keep voltage drop under 3% for branch circuits and under 5% for the total feeder-plus-branch combined. Use a dedicated voltage drop calculator from a major wire manufacturer to find the exact upsized wire required for long runs. When voltage drop demands a larger wire than the ampacity table, the voltage drop size always wins.
