The most common wire AWG sizes for residential branch circuits are 14 AWG (15A), 12 AWG (20A), and 10 AWG (30A). For larger feeders, 4 AWG copper handles 85A, while 2 AWG handles 115A. You must always size your overcurrent protective device (breaker) to the lowest ampacity rating of the wire, termination, or device in the circuit. Below is the definitive reference for sizing copper and aluminum conductors based on the National Electrical Code (NEC).
How to Read the NEC Wire AWG Sizes Table
The ampacity table below is derived from NEC Table 310.16 (formerly 310.15(B)(16)). It lists the allowable ampacities for insulated conductors rated up to 2000 volts. To use it correctly, you must understand the temperature columns and the termination rules outlined in NEC 110.14(C).
- 60°C Column: Use this for circuits rated 100A or less, or for wire sizes 14 AWG through 1 AWG, unless you can verify that both the wire insulation and the equipment terminals are explicitly rated for 75°C. Since most modern breakers and receptacles are 75°C rated, you can often use the 75°C column, but the 60°C column remains the conservative legal baseline for small residential branch circuits.
- 75°C Column: Use this for circuits over 100A, or wire sizes larger than 1 AWG, provided the terminations are rated for 75°C.
- 90°C Column: Never use this column to size a breaker. The 90°C column is strictly used as the starting baseline for applying ambient temperature and conduit bundling derating factors.
The Master Wire AWG Sizes and Ampacity Chart
The following spec-sheet-table provides the allowable ampacities for common residential and light commercial wire sizes. Values assume an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway or cable.
| AWG / kcmil | Copper 60°C (A) | Copper 75°C (A) | Copper 90°C (A) | Aluminum 75°C (A) | Max Standard Breaker (Copper) |
|---|---|---|---|---|---|
| 14 | 15 | 20 | 25 | — | 15A |
| 12 | 20 | 25 | 30 | — | 20A |
| 10 | 30 | 35 | 40 | — | 30A |
| 8 | 40 | 50 | 55 | 40 | 40A / 50A* |
| 6 | 55 | 65 | 75 | 50 | 60A |
| 4 | 70 | 85 | 95 | 65 | 80A / 90A* |
| 3 | 85 | 100 | 110 | 75 | 100A |
| 2 | 95 | 115 | 130 | 90 | 115A / 125A* |
| 1 | 110 | 130 | 145 | 100 | 125A |
| 1/0 | 125 | 150 | 170 | 120 | 150A |
| 2/0 | 145 | 175 | 195 | 135 | 175A |
| 3/0 | 165 | 200 | 225 | 155 | 200A |
| 4/0 | 195 | 230 | 260 | 180 | 225A / 250A* |
*Note: Breaker sizes marked with an asterisk rely on the NEC 240.4(B) "next-size-up" rule, which allows you to round up to the next standard breaker size if the calculated load does not exceed the wire's ampacity. For 14, 12, and 10 AWG, NEC 240.4(D) strictly prohibits next-size-up; you must use the exact 15A, 20A, or 30A limits.
Quick-Jump: Most Queried AWG Sizes for Home Wiring
Bookmark this section for the five most common residential circuit scenarios. These assume standard NM-B (Romex) cable, which is limited to the 60°C column regardless of the 90°C rating of the individual THHN conductors inside it.
- 14 AWG (15A Breaker): General lighting circuits in bedrooms, living rooms, and hallways. Maximum continuous load: 12A.
- 12 AWG (20A Breaker): Standard kitchen, bathroom, and garage receptacles. Required for any 20A small-appliance branch circuit. Maximum continuous load: 16A.
- 10 AWG (30A Breaker): Electric water heaters, window AC units, and standard electric dryers (when paired with a 10/3 cable and a NEMA 10-30 or 14-30 receptacle). Maximum continuous load: 24A.
- 6 AWG (60A Breaker): Electric ranges, ovens, and backup generator inlet boxes. Use 6/3 NM-B for runs up to 50 feet.
- 4 AWG (85A/90A Breaker): 100A subpanel feeders (using THHN in conduit) or heavy-duty EV charger circuits (hardwired 80A chargers require 4 AWG copper at 75°C terminations).
Derating Factors: When Your Base Ampacity Drops
The ampacities in the master table assume ideal conditions: 30°C ambient temperature and no more than three current-carrying conductors in a conduit. Real-world jobsites rarely match this. When you bundle wires or run them through hot attics, you must apply derating factors per NEC 310.15.
How derating modifies the base value: Derating calculations always begin with the 90°C column, even if your terminations are only rated for 60°C. However, the final derated ampacity cannot exceed the base ampacity of the temperature column that applies to your terminations (usually 60°C or 75°C).
Worked Example: You are pulling four 12 AWG THHN current-carrying conductors through a conduit in a garage where the ambient temperature is 30°C. 1. Base 90°C ampacity for 12 AWG = 30A. 2. NEC Table 310.15(C)(1) dictates an 80% adjustment factor for 4-6 conductors. 3. 30A × 0.80 = 24A. 4. Because 24A is greater than the 60°C base limit of 20A, the wire is still legally permitted to be protected by a 20A breaker.
Failure Scenario: If you pull 10 conductors in that same conduit, the adjustment factor drops to 50%. 30A × 0.50 = 15A. Because 15A is now less than the 20A termination limit, you must either drop your breaker to 15A or upsize the wire to 10 AWG (90°C base of 40A × 0.50 = 20A).
Decision Path: Picking the Right Wire AWG Size
Stop guessing. Follow this decision-tree-table to terminate your sizing process with a concrete pick. This path assumes a standard residential 120V/240V system with 75°C rated terminals.
| Step | Action / Calculation | Example (Continuous Load) | Example (Non-Continuous Load) |
|---|---|---|---|
| 1. Determine Base Load | Calculate the maximum expected current draw of the appliance or circuit. | 16 Amps (e.g., server rack or space heater running 3+ hours) | 12 Amps (e.g., TV and gaming console) |
| 2. Apply 125% Rule | If the load is continuous (runs for 3 hours or more), multiply by 1.25. If non-continuous, multiply by 1.0. | 16A × 1.25 = 20A minimum circuit ampacity | 12A × 1.0 = 12A minimum circuit ampacity |
| 3. Select Wire AWG | Find the smallest AWG in the Master Table (60°C or 75°C column) that equals or exceeds the Step 2 value. | 20A requires 12 AWG Copper (60°C column) | 12A requires 14 AWG Copper (60°C column) |
| 4. Select Breaker | Pick the standard breaker size that matches the wire's ampacity limit (or next-size-up if >10 AWG and load permits). | 20A Breaker | 15A Breaker |
| FINAL PICK | Buy the wire and breaker. | 12 AWG wire, 20A breaker | 14 AWG wire, 15A breaker |
What This Table Cannot Tell You
While NEC Table 310.16 is the gold standard for thermal ampacity (preventing the wire from melting or degrading its insulation), it is blind to three critical physical realities of your installation:
- Voltage Drop: The NEC only provides informational notes regarding voltage drop (recommending a max 3% drop on branch circuits and 5% total). If you are running a 12 AWG wire 150 feet to a 15A load, the wire will not overheat, but you will lose roughly 9.6 volts. Your equipment will see 110V instead of 120V, causing motors to run hot and electronics to brown out. Fix: Upsize to 10 AWG or 8 AWG for long runs.
- Conduit Fill Capacity: Ampacity tells you how much current a wire can carry; NEC Chapter 9, Table 1 tells you how many wires physically fit inside a conduit. You cannot shove six 6 AWG THHN wires into a 3/4-inch EMT conduit, even if the derating math technically allows the ampacity.
- Short-Circuit Let-Through Current: Ampacity tables assume normal operating conditions. They do not account for the massive magnetic and thermal forces generated during a dead-bolt short circuit. For high-fault-current environments (like main service entrances near large transformers), you must verify the wire's bracing and the breaker's AIC (Ampere Interrupting Capacity) rating.
Always verify your final wire AWG sizes against local amendments. While the NEC provides the baseline, your local Authority Having Jurisdiction (AHJ) has the final say on permitted materials and sizing methods in your specific municipality.
