For standard 120V/240V residential branch circuits, the baseline rule is simple: 14 AWG solid copper handles 15 amps, 12 AWG handles 20 amps, and 10 AWG handles 30 amps when using the 60°C column of NEC Table 310.16. While the National Electrical Code (NEC) ampacity tables do not explicitly separate solid from stranded wire for these smaller gauges, 14, 12, and 10 AWG are almost exclusively manufactured and installed as solid copper in NM-B (Romex) and THHN because it is cheaper, easier to terminate on standard receptacle screws, and holds its shape in boxes.
The Solid Copper Wire Gauge Chart (NEC Table 310.16)
The data below is extracted directly from NEC Table 310.16 (2023/2026 editions), which governs allowable ampacities for insulated conductors rated up to 2000 volts. How to read this table: The AWG column lists the physical wire size. The temperature columns (60°C, 75°C, 90°C) represent the thermal rating of the wire's insulation and the terminals it connects to. You must select the ampacity based on the lowest temperature rating of any component in the circuit (wire, breaker, or receptacle). For solid copper, we focus primarily on 14 through 8 AWG, as 6 AWG and larger are practically always stranded due to the extreme physical stiffness of thick solid copper.
| AWG Size (Solid Copper) | 60°C Column (140°F) | 75°C Column (167°F) | 90°C Column (194°F) |
|---|---|---|---|
| 14 AWG | 15A | 20A* | 25A* |
| 12 AWG | 20A | 25A | 30A |
| 10 AWG | 30A | 35A | 40A |
| 8 AWG | 40A | 50A | 55A |
*NEC 240.4(D) strictly limits 14 AWG overcurrent protection to 15A, and 12 AWG to 20A for standard residential branch circuits, regardless of the higher ampacities shown in the 75°C and 90°C columns.
Quick-Jump Rows for Common Residential Circuits
Bookmark this section for your most frequent jobsite and workbench lookups. These are the default configurations for 95% of residential solid copper wiring.
- 14 AWG Solid (White NM-B): 15 Amps max. Used for general lighting, bedroom outlets, and low-draw living room circuits. Pro-tip: Many electricians refuse to use 14 AWG anymore, defaulting to 12 AWG to prevent future homeowners from swapping a 15A breaker for a 20A breaker and causing a fire.
- 12 AWG Solid (Yellow NM-B): 20 Amps max. The undisputed standard for kitchen small-appliance circuits, bathroom GFCI receptacles, garage outlets, and outdoor weatherproof receptacles.
- 10 AWG Solid (Orange NM-B): 30 Amps max. Used for dedicated 240V electric water heaters, window AC units, and heavy-duty 120V RV receptacles. Note that 10 AWG solid is quite stiff; use deep 1-gang or 4-square boxes to accommodate the bending radius.
- 8 AWG Solid: 40 Amps max. Rarely used in solid form. If you need 8 AWG for a 40A EV charger or cooktop, buy stranded THHN or stranded SER cable. Pulling solid 8 AWG through conduit bends is a knuckle-busting nightmare.
Which Temperature Column Applies to Your Installation?
The most common mistake DIYers make when reading a solid copper wire gauge chart is looking exclusively at the 90°C column because it offers the highest ampacity. Here is how to legally and safely pick your column:
You can only use a higher temperature column if every single termination point in the circuit is rated for that temperature. If your wire is 90°C THHN, but the receptacle is only rated for 60°C, you must use the 60°C ampacity column.
- The 60°C Column: Applies to almost all standard NM-B (Romex) cable, older breakers, and standard 15A/20A duplex receptacles. If you are wiring standard outlets and lights in residential walls, this is your column.
- The 75°C Column: Applies to THHN/THWN-2 wires pulled in conduit terminating in modern, commercially rated panels and heavy-duty 75°C-rated breakers or lugs. You can use this column for feeder wires or subpanel connections.
- The 90°C Column: According to the Copper Development Association and NEC guidelines, the 90°C column is almost exclusively used as a starting point for derating calculations. You do not use the 90°C ampacity to size your breaker.
Derating Factors: When the Base Ampacity Drops
The ampacities in the chart above assume an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together. When you exceed these conditions, the wire cannot dissipate heat effectively, and you must apply derating factors.
How derating modifies the base value: If you pull four 12 AWG THHN wires through a single conduit (e.g., two hots, one neutral, one ground for a multi-wire branch circuit or a 240V circuit with a neutral), the ground does not count as a current-carrying conductor. You have 3 current-carrying conductors. No derating needed. But if you add a second circuit to that same conduit (now 4 current-carrying conductors), NEC Table 310.15(C)(1) requires you to derate to 80%.
Worked Example: You have 12 AWG THHN (90°C rating = 30A base). You pull 5 current-carrying conductors in a conduit. The derating factor for 4-6 conductors is 80%.
Calculation: 30A × 0.80 = 24A.
Result: Your 12 AWG wire is now legally limited to 24A. Since NEC 240.4(D) caps 12 AWG at 20A anyway, you can still protect it with a 20A breaker. However, if you had 6 current-carrying conductors (derated to 50%), 30A × 0.50 = 15A. You would be forced to upsize to 10 AWG wire to maintain a 20A circuit.
Decision Path: Pick Your Exact Wire Gauge Now
Stop guessing. Use this decision-tree-table to terminate your planning phase and pick the exact wire to buy.
| Your Application & Load | Run Length | Concrete Pick (Buy This) |
|---|---|---|
| General lighting & 15A bedroom outlets | Under 50 ft | 14/2 NM-B (15A Breaker) |
| Kitchen, bathroom, garage, or outdoor 20A receptacles | Under 50 ft | 12/2 NM-B (20A Breaker) |
| Standard 20A circuit (Kitchen/Bath) | 50 ft to 100 ft | 10/2 NM-B (Upsized for voltage drop, 20A Breaker) |
| 240V Electric Water Heater (up to 4500W / 18.75A) | Any standard run | 10/2 NM-B (30A Breaker) |
| THHN in conduit for a 20A circuit with 4+ current-carrying wires | Any | 10 AWG THHN (Derates safely to 20A+) |
What This Chart Cannot Tell You
An ampacity chart is a thermal limit document, not a complete engineering guide. Here is what the solid copper wire gauge chart leaves out, which will burn you if ignored:
- Voltage Drop: The NEC recommends keeping voltage drop under 3% for branch circuits and 5% overall. If you are running a 12 AWG circuit 120 feet to a shed to run a 15A table saw, the wire won't melt (it's under the 20A thermal limit), but the voltage at the shed will drop below 110V, causing the saw motor to overheat and trip its internal thermal protector. For runs over 75 feet, always upsize one gauge.
- Conduit Fill Capacity: NEC Chapter 9, Table 1 limits conduit fill to 40% for three or more wires. You might be legally allowed to use 14 AWG based on ampacity, but if you are pulling 8 wires through a 1/2-inch EMT conduit, they physically will not fit without jamming and tearing the insulation.
- Physical Stiffness and Box Fill: Solid copper work-hardens and becomes incredibly stiff. Bending three 10 AWG solid wires into a standard single-gang device box to attach a 30A receptacle is a physical struggle and often exceeds NEC box fill volume limits. Always calculate cubic inch box fill before rough-in.
The Final Default: When in doubt on a standard 120V residential branch circuit under 50 feet, default to 12 AWG solid copper (12/2 NM-B). It safely covers both 15A and 20A loads, minimizes voltage drop, accommodates future load increases, and costs only pennies more per foot than 14 AWG. Terminate it on a 20A breaker and move on to the next task.
