For standard US residential branch circuits using copper THHN/THWN-2 wire, use 14 AWG for 15A circuits, 12 AWG for 20A circuits, and 10 AWG for 30A circuits. This baseline assumes standard 75°C terminations, an ambient temperature of 30°C (86°F), and no more than three current-carrying conductors in a single raceway. If your run exceeds 100 feet, or you are bundling more than three wires in a conduit, you must adjust these sizes using the derating rules below.

How to Read the NEC AWG Wire Table (And Which Column to Use)

The most common mistake DIYers and junior electricians make is reading the wrong temperature column on the National Electrical Code (NEC) ampacity charts. Modern wire insulation like THHN is rated for 90°C, which tempts builders to use the 90°C column to squeeze more current out of a smaller wire. Do not do this.

Here is how to read the columns correctly:

  • 60°C Column: Use this for 14, 12, and 10 AWG conductors. Under NEC 240.4(D), these small conductors are strictly hard-capped at 15A, 20A, and 30A respectively, regardless of their 90°C insulation rating. You also use this column if you are terminating on older equipment or devices explicitly marked for 60°C only.
  • 75°C Column: This is your default working column for 8 AWG and larger. Most modern residential breakers, lugs, and receptacles are rated for 75°C terminations (per NEC 110.14(C)).
  • 90°C Column: You only use this column for derating calculations (adjusting for high ambient heat or conduit bundling). The final derated ampacity must still be terminated based on the 60°C or 75°C column limits.
Quick-Jump Bookmark Rows: If you are wiring standard home circuits, you only need to memorize three rows: 14 AWG (15A), 12 AWG (20A), and 10 AWG (30A). For heavy appliances, memorize 6 AWG (50A range) and 2 AWG (100A subpanel feeder).

Complete Copper AWG Ampacity Chart (NEC Table 310.16)

The following data is extracted from NEC Table 310.16 (formerly 310.15(B)(16)) for copper conductors with temperature ratings of 60°C, 75°C, and 90°C, based on an ambient temperature of 30°C. For standard home wiring, refer primarily to the 60°C and 75°C columns.

AWG Size 60°C (TW, UF) 75°C (THHW, THW) 90°C (THHN, THWN-2) Common Residential Application
14 AWG15A20A25A15A Lighting/Receptacle Circuits
12 AWG20A25A30A20A Kitchen/Bath/Outdoor Circuits
10 AWG30A35A40A30A Dryer / RV Receptacle
8 AWG40A50A55A40A-50A Range / EV Charger
6 AWG55A65A75A50A-60A Subpanel Feeder / Spa
4 AWG70A85A95A70A-85A Heavy Subpanel Feeder
3 AWG85A100A110A100A Subpanel Feeder
2 AWG95A115A130A100A-125A Main Feeder
1 AWG110A130A145A125A-150A Subpanel Feeder
1/0 AWG125A150A170A150A Main Service Feeder
2/0 AWG145A175A195A150A-200A Main Service Feeder
3/0 AWG165A200A225A200A Main Service Entrance
4/0 AWG195A230A260A200A-225A Heavy Service Entrance

Derating: When the Base Table Lies to You

The AWG wire table above assumes perfect conditions: 30°C ambient air and no more than three current-carrying conductors (CCCs) in a raceway. When you deviate from this, you must apply derating factors, or the wire will overheat and melt the insulation inside the wall.

1. Conduit Bundling (NEC Table 310.15(C)(1))
If you pull four to six CCCs through a single conduit, you must multiply the wire's 90°C ampacity by 80%. If you pull seven to nine CCCs, multiply by 70%. Note: Grounding wires and neutral wires that only carry unbalanced load do not count as CCCs.

2. Ambient Temperature (NEC Table 310.15(B)(1))
If your wire runs through an attic that reaches 110°F (43°C), you must multiply the 90°C ampacity by 0.87. If it runs across a roof deck where temperatures hit 122°F (50°C), the multiplier drops to 0.82.

Bench Example: You pull four 12 AWG THHN current-carrying conductors through a single conduit for a multi-wire branch circuit. The 80% bundling derating factor drops your 30A (90°C column) capacity to 24A. However, because NEC 240.4(D) hard-caps 12 AWG at a 20A breaker, your final breaker size remains 20A. The derating math didn't force an upsizing here, but if you were using 8 AWG wire (55A at 90°C), an 80% derate drops it to 44A, forcing you to use a 40A breaker instead of a 50A breaker.

What the AWG Wire Table Cannot Tell You

An ampacity chart only tells you the thermal limit of the wire insulation. It completely ignores three critical real-world failure points:

  1. Voltage Drop: The NEC doesn't strictly mandate voltage drop limits for branch circuits, but it highly recommends a maximum 3% drop on branch circuits and 5% total from the utility to the furthest outlet. If you are running a 12 AWG wire to a 15A shed 150 feet away, the wire won't melt, but the voltage at the shed will drop below 114V, causing motors to stall and overheat. Rule of thumb: Upsize the wire by one AWG step for every 100 feet of run beyond 50 feet.
  2. Conduit Fill Limits: You might calculate that three 4 AWG wires are perfect for a 100A feeder, but NEC Chapter 9, Table 1 limits conduit fill to 40% for three or more wires. You physically cannot pull three 4 AWG THHN wires through a 1/2-inch EMT conduit without jamming and tearing the insulation.
  3. Motor Starting Currents: A 5 HP air compressor might draw 20A running, but the locked-rotor starting current can spike to 60A for a fraction of a second. The AWG table doesn't account for this. NEC Article 430 requires you to size the wire at 125% of the motor's full-load current, and the breaker much higher to accommodate the startup spike.

Decision Path: Pick Your Exact Wire Size

Stop guessing. Use this decision matrix to terminate your sizing debate and pick the exact copper wire gauge for your next pull. All recommendations assume standard copper THHN/THWN-2 in a residential environment.

If Your Load / Application Is... And Your Run Length Is... Then Your Exact Pick Is...
Standard 15A lighting / bedroom outlets Under 50 feet 14 AWG (15A Breaker)
Standard 15A lighting / bedroom outlets 50 to 100 feet 12 AWG (15A Breaker)
20A Kitchen, Bath, or Garage GFCI circuits Under 75 feet 12 AWG (20A Breaker)
20A Kitchen, Bath, or Garage GFCI circuits 75 to 120 feet 10 AWG (20A Breaker)
30A Electric Dryer (4-wire, 120/240V) Under 50 feet 10 AWG (30A Breaker)
40A to 50A EV Charger / Electric Range Under 60 feet 6 AWG (50A Breaker)
100A Subpanel Feeder (120/240V) Under 100 feet 3 AWG (100A Breaker)
100A Subpanel Feeder (120/240V) 100 to 150 feet 1 AWG (100A Breaker)
200A Main Service Entrance Under 75 feet 2/0 AWG (200A Main)

Default Recommendation: If your specific scenario is not listed above, or if you are unsure about future load expansions, default to 12 AWG for all 15A and 20A general-purpose branch circuits. The material cost difference between 14 AWG and 12 AWG NM-B cable is roughly $15 per 250-foot roll, but the 12 AWG gives you a 33% headroom buffer for voltage drop and allows you to upgrade the breaker to 20A later without tearing open the drywall.