When sizing wire for a branch circuit or feeder, the most common residential AWG sizes are 14 AWG (15A), 12 AWG (20A), and 10 AWG (30A). These baseline values come directly from the 60°C column of NEC Table 310.16. However, pulling the right wire from the spool requires more than just matching the breaker size to the base ampacity. You must account for termination temperature limits, conduit bundling derating, and voltage drop over distance.
This reference guide provides the complete copper amp chart, explains exactly which temperature column applies to your installation, and gives you a concrete decision tree to pick the right wire and breaker without a second trip to the supply house.
How to Read the NEC AWG Ampacity Chart
The most common mistake DIYers and junior electricians make is looking at the 90°C column because modern THHN/THWN-2 wire is rated for 90°C, and assuming they can use that higher ampacity. You usually cannot.
Under NEC 110.14(C), the ampacity of a wire is limited by the lowest temperature rating of any connected termination, device, or conductor. Since standard residential breakers, receptacles, and switches are typically rated for 60°C or 75°C, you must follow these rules:
- The 60°C Column: Use this column for circuits rated 100A or less, or for wire sizes 14 AWG through 1 AWG. This is your baseline for standard residential branch circuits.
- The 75°C Column: Use this column for circuits rated over 100A, or wire sizes larger than 1 AWG, provided the equipment terminations are explicitly marked for 75°C (most modern panels and heavy-duty disconnects are).
- The 90°C Column: You can only use this column as the starting baseline for derating calculations (adjusting for ambient temperature or bundling multiple wires in a conduit). The final derated ampacity must still be compared against the 60°C or 75°C termination limits.
The Master AWG Amp Chart (Copper, THHN/THWN-2)
Below is the complete ampacity table for copper conductors. Bookmark the quick-jump list below for the most frequently queried residential and light-commercial sizes.
• 14 AWG: 15A Max (Lighting/Receptacles)
• 12 AWG: 20A Max (Kitchen/Bath/Appliance)
• 10 AWG: 30A Max (Dryers/Water Heaters)
• 8 AWG: 40A Max (Cooktops/Heat Strips)
• 6 AWG: 55A Base / 60A Breaker (Ranges/Subpanels)
• 4 AWG: 70A Max (Large Subpanels)
• 2 AWG: 95A Base / 100A Breaker (100A Subpanels)
| AWG Size | 60°C (140°F) | 75°C (167°F) | 90°C (194°F) | Standard Max Breaker |
|---|---|---|---|---|
| 14 | 15A | 20A | 25A | 15A |
| 12 | 20A | 25A | 30A | 20A |
| 10 | 30A | 35A | 40A | 30A |
| 8 | 40A | 50A | 55A | 40A |
| 6 | 55A | 65A | 75A | 60A* |
| 4 | 70A | 85A | 95A | 70A |
| 3 | 85A | 100A | 110A | 90A* |
| 2 | 95A | 115A | 130A | 100A* |
| 1 | 110A | 130A | 145A | 110A |
| 1/0 | 125A | 150A | 170A | 125A |
| 2/0 | 145A | 175A | 195A | 150A |
| 3/0 | 165A | 200A | 225A | 175A |
| 4/0 | 195A | 230A | 260A | 200A |
*Note: NEC 240.4(B) allows you to round up to the next standard breaker size if the exact ampacity does not correspond to a standard breaker, provided the load is not continuous. NEC 240.4(D) strictly limits 14 AWG to 15A, 12 AWG to 20A, and 10 AWG to 30A, overriding the round-up rule.
Derating: How Bundling and Temperature Shrink Capacity
The amp chart above assumes you have no more than three current-carrying conductors in a raceway and an ambient temperature of 30°C (86°F). When you exceed these conditions, the wire cannot dissipate heat as effectively, and you must derate its capacity.
This is where the 90°C column becomes useful. According to the NFPA National Electrical Code, you apply derating factors to the 90°C ampacity, then compare the result to the termination limits (60°C or 75°C). You must use the lowest resulting number.
You are pulling four 12 AWG THHN wires (two hots, one neutral, one ground) through a single conduit for a multi-wire branch circuit. Only the two hots and the neutral are current-carrying (3 conductors). Wait, if it's a standard 120V MWBC, the neutral carries the unbalanced load and counts. Let's say you have four current-carrying conductors in the pipe.
1. Base 90°C ampacity for 12 AWG = 30A.
2. NEC Table 310.15(C)(1) states 4-6 conductors require an 80% derating factor.
3. 30A × 0.80 = 24A derated ampacity.
4. Compare 24A to the 60°C termination limit for 12 AWG (20A). The 60°C limit is lower.
Result: Your final allowable ampacity is 20A. You can still safely use a 20A breaker, but you have zero headroom. If you added a fifth current-carrying wire, the derating would drop to 70% (21A), forcing you to upsize to 10 AWG.
Decision Tree: Picking the Right AWG and Breaker
Use this decision-tree-table to terminate your planning phase and pick the exact materials for your next pull. These recommendations assume standard residential terminations (60°C/75°C) and runs under 100 feet.
| If Your Load / Application Is... | And Your Max Continuous Draw Is... | Buy This Wire (Copper THHN/NM-B) | Install This Breaker |
|---|---|---|---|
| General Lighting / Bedroom Receptacles | ≤ 12A | 14 AWG | 15A Standard |
| Kitchen / Bath / Garage Receptacles | ≤ 16A | 12 AWG | 20A Standard |
| Electric Dryer / Window AC / Water Heater | ≤ 24A | 10 AWG | 30A Standard |
| Electric Cooktop / EV Charger (Level 2) | ≤ 32A | 8 AWG | 40A Standard |
| Full-Size Electric Range / Oven | ≤ 40A | 6 AWG | 50A Standard |
| 100A Subpanel Feeder (Short Run) | ≤ 80A Continuous | 2 AWG (or 1/0 AL) | 100A Main Lug/Breaker |
What This AWG Amp Chart Cannot Tell You
The amp chart dictates how much current a wire can carry before the insulation melts or the breaker trips. It does not account for voltage drop. According to the Copper Development Association and NEC informational notes, branch circuits should be sized to limit voltage drop to a maximum of 3% for optimal efficiency and equipment lifespan.
If you are running a 20A circuit to a detached garage 150 feet away, the amp chart says 12 AWG is perfectly fine. However, at 150 feet under a full 20A load, 12 AWG copper will experience a voltage drop of roughly 7.5% (dropping your 120V supply down to 111V). This will cause motors to overheat, lights to dim, and sensitive electronics to brown out.
The Fix: For runs exceeding 75-100 feet, you must calculate voltage drop and upsize the wire, even if the breaker size remains the same. For the 150-foot garage run, you would upsize to 8 AWG copper to keep the drop under 3%, while still terminating on a 20A breaker.
Default Recommendation: If your distance calculation lands on a borderline voltage drop (e.g., 3.1%), always upsize by one full AWG step. The marginal increase in copper cost is negligible compared to the cost of a failed compressor motor or the headache of pulling a new feeder line later. When in doubt on long runs, buy the heavier gauge.
