The Standard Electrical Wiring Size Chart (NEC Table 310.16)
This chart lists the allowable ampacity for copper conductors rated up to 2000 volts, with up to three current-carrying conductors in a raceway or cable, at an ambient temperature of 30°C (86°F). The columns represent the temperature rating of the wire insulation. Always cross-reference the insulation type printed on the wire jacket (e.g., THHN, THWN-2, NM-B) with these columns. According to the National Fire Protection Association (NFPA), this table is the baseline for all residential and commercial wire sizing before derating factors are applied.
Quick-Jump to Most Queried Sizes:
- 14 AWG (15A Standard Lighting/Outlets)
- 12 AWG (20A Kitchen/Bath/Garage)
- 10 AWG (30A Dryers/RVs)
- 6 AWG (50A Ranges/Welders)
- 3 AWG (100A Subpanel Feeders)
| AWG Size | 60°C (140°F) | 75°C (167°F) | 90°C (194°F) |
|---|---|---|---|
| 14 | 15A | 20A | 25A |
| 12 | 20A | 25A | 30A |
| 10 | 30A | 35A | 40A |
| 8 | 40A | 50A | 55A |
| 6 | 55A | 65A | 75A |
| 4 | 70A | 85A | 95A |
| 3 | 85A | 100A | 115A |
| 2 | 95A | 115A | 130A |
| 1 | 110A | 130A | 145A |
| 1/0 | 125A | 150A | 170A |
| 2/0 | 145A | 175A | 195A |
| 3/0 | 165A | 200A | 225A |
| 4/0 | 195A | 230A | 260A |
Which Column Applies to Your Installation?
The most common mistake DIYers make is looking at the 90°C column because they bought THHN wire, then sizing their breaker to that higher number. NEC Article 110.14(C) dictates that your wire ampacity is ultimately limited by the temperature rating of the terminals the wire connects to, not just the wire insulation.
- Circuits 100A or less (or using 14-1 AWG wire): Assume terminals are rated 60°C unless the equipment is explicitly stamped '75°C'. Most standard 15A and 20A receptacles fall here. Default to the 60°C column.
- Circuits over 100A (or using 1/0 AWG and larger): Panelboard lugs and heavy-duty disconnects are universally rated 75°C. Use the 75°C column.
- The 90°C Column: You only use this column to calculate derating adjustments (bundling and high ambient heat). The final derated ampacity must still be high enough to support the breaker size dictated by the 60°C or 75°C terminal limits.
Decision Path: Picking Your Exact Wire and Breaker
Use this decision tree to lock in your exact materials for standard residential branch circuits and feeders. This assumes standard copper wire and standard residential loads.
| Scenario | Max Continuous Load | Breaker Size | Concrete Wire Pick (Copper) |
|---|---|---|---|
| Standard Bedroom/Living Room Outlet | 12A | 15A | 14 AWG NM-B (60°C rated) |
| Kitchen/Bath/Garage Small Appliance | 16A | 20A | 12 AWG NM-B (60°C rated) |
| Electric Dryer or RV Hookup | 24A | 30A | 10 AWG (NM-B or THHN) |
| Electric Range or Welder Receptacle | 40A | 50A | 6 AWG THHN/THWN-2 |
| 100A Subpanel Feeder (75°C Terminals) | 80A | 100A | 3 AWG THHN/THWN-2 or 1 AWG Aluminum |
How Derating Modifies Your Base Ampacity
The chart above assumes perfect conditions: 30°C (86°F) ambient air and no more than three current-carrying conductors bundled together. Real-world jobsites rarely match this. When conditions change, you must apply derating multipliers to the 90°C column (even if your terminals are rated 60°C) to ensure the wire insulation doesn't melt inside the conduit.
1. Bundling Derating (NEC Table 310.15(C)(1))
If you pull 4 to 6 current-carrying conductors in a single conduit, multiply the 90°C base ampacity by 80%. (Note: Ground wires and neutrals in balanced 240V-only circuits do not count as current-carrying).
2. Ambient Temperature Derating (NEC Table 310.15(B)(1))
If your conduit runs through a 40°C (104°F) attic, multiply the 90°C base ampacity by 0.91.
- Base 90°C ampacity for 12 AWG = 30A.
- Bundling derate (4-6 conductors per circuit pair, but let's assume 4-6 total in the pipe for this example) = 80%. (30A x 0.80 = 24A).
- Temperature derate (40°C factor = 0.91). (24A x 0.91 = 21.8A).
- Result: Your wire can safely carry 21.8A. Since NEC 240.4(D) strictly limits 12 AWG overcurrent protection to 20A max, you are clear to use a 20A breaker. If the math resulted in 18A, you would be forced to upsize to 10 AWG wire.
What This Chart Cannot Tell You
The electrical wiring size chart guarantees the wire won't overheat and start a fire under a specific load. It does not guarantee the equipment at the end of the wire will function correctly. For that, you must calculate voltage drop.
According to industry standards and resources like the Southwire voltage drop guidelines, a 3% maximum voltage drop is the accepted threshold for branch circuits, and 5% total for feeder plus branch combined. On a 120V circuit, 3% is 3.6V. If you run a 12 AWG wire 150 feet to a 15A space heater, the wire won't melt (it's well under the 20A limit), but the voltage at the heater will drop below 115V, causing poor performance and potential motor burnout. For long runs, use the formula VD = (2 x K x I x D) / CM (where K=12.9 for copper, I=load amps, D=one-way distance, CM=circular mils of the wire) and upsize the wire accordingly, regardless of the ampacity chart.
The Final Default Recommendation: Stop guessing terminal ratings. For all indoor staple-up branch circuits, buy 60°C rated NM-B (Romex) and use the 60°C column. For all conduit pulls, buy 90°C rated THHN/THWN-2 copper wire to give yourself maximum derating headroom, but terminate your 15A-50A breakers and receptacles using the 60°C ampacity limits. For any subpanel feeder over 100A, use the 75°C column and torque your lugs to the manufacturer's exact inch-pound spec.
