When sizing solid copper wire for residential and commercial branch circuits, the numbers that matter are dictated by NFPA 70 (the National Electrical Code). The solid wire gauge chart below is derived directly from NEC Table 310.16 (formerly 310.15(B)(16)), which establishes the allowable ampacities for insulated conductors rated up to 2000 volts.

Before pulling wire, you must understand how to read this table. The NEC provides three temperature columns (60°C, 75°C, and 90°C). Your final breaker size is almost always limited by the lowest temperature rating of any component in the circuit—including the wire, the breaker terminals, and the receptacle. Furthermore, while ampacity applies to both solid and stranded wire equally, physical availability differs: solid wire is standard in NM-B (Romex) cable up to 8 AWG, but THHN in conduit transitions to stranded at larger sizes due to pulling stiffness.

The Master Solid Wire Gauge Chart (NEC Table 310.16)

The following table covers the most queried solid wire sizes for branch circuits. Source Standard: NFPA 70 (NEC) Table 310.16, Copper Conductors, 30°C (86°F) Ambient Temperature, up to 3 current-carrying conductors in a raceway.

AWG Size 60°C (140°F) 75°C (167°F) 90°C (194°F) Solid Wire Availability (THHN / NM-B)
14 AWG 15A 20A 25A Common in both THHN and NM-B
12 AWG 20A 25A 30A Common in both THHN and NM-B
10 AWG 30A 35A 40A Common in both THHN and NM-B
8 AWG 40A 50A 55A Rare in THHN (too stiff); Standard in NM-B
6 AWG 55A 65A 75A Stranded in THHN; Solid available in some NM-B
4 AWG 70A 85A 95A Exclusively Stranded (THHN/XHHW)
Bookmark Quick-Jump: For standard 15A lighting circuits, reference 14 AWG. For 20A kitchen and bathroom receptacles, reference 12 AWG. For 30A dryer or RV outlets, reference 10 AWG.

Which Temperature Column Actually Applies to Your Install?

A common jobsite mistake is looking at the 90°C column and assuming a 12 AWG wire can be placed on a 30A breaker because the 90°C column reads "30A". This violates NEC 110.14(C) and NEC 240.4(D). Here is how to select the correct column:

  • The 60°C Column (The Default for Small Wires): For circuits rated 100A or less, or for wire sizes 14 AWG through 10 AWG, you must use the 60°C column to determine your maximum breaker size. This is because standard residential receptacles and breaker terminals are typically rated for 60°C or 75°C, and the NEC defaults to the lowest common denominator for small conductors.
  • The 75°C Column (The Default for Larger Wires): For wire sizes 8 AWG and larger on circuits over 100A, or when terminating to equipment explicitly marked "75°C" (like modern subpanel lugs and heavy-duty contactors), use the 75°C column.
  • The 90°C Column (Derating Only): You can almost never use the 90°C column to size your breaker. Its sole practical purpose is to provide a higher base number for derating calculations (explained below) before you apply the final termination temperature limits.

Derating: When Your Base Ampacity Shrinks

The chart above assumes a maximum 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 as efficiently, and you must reduce (derate) its allowable ampacity.

Derating calculations always start with the 90°C column value, regardless of your termination limits. Multiply the 90°C ampacity by the correction factor, then verify the result does not exceed the 60°C or 75°C termination limit.

Condition Correction Factor Example: 12 AWG THHN in Conduit (Base 90°C = 30A)
4 to 6 current-carrying conductors in one raceway 80% 30A × 0.80 = 24A (Still safe for a 20A breaker)
7 to 9 current-carrying conductors in one raceway 70% 30A × 0.70 = 21A (Still safe for a 20A breaker)
Ambient temp 41-45°C (105-113°F) e.g., hot attic 87% (for 90°C wire) 30A × 0.87 = 26.1A (Safe for a 20A breaker)
10 to 20 current-carrying conductors 50% 30A × 0.50 = 15A (Must drop to a 15A breaker or upsize to 10 AWG)
Neutral and Ground Counting: In a standard multi-wire branch circuit (MWBC) or single-phase 120V/240V circuit, the equipment grounding conductor (bare/green) is never counted as a current-carrying conductor. The neutral (white) is counted if it carries unbalanced current from nonlinear loads (like LED drivers or computers), per NEC 310.15(C)(1).

What This Chart Cannot Tell You

Ampacity charts only solve for thermal limits (preventing the wire insulation from melting). They do not account for three critical real-world variables:

  1. Voltage Drop: NEC 310.16 does not enforce voltage drop; it only enforces heat. However, NEC 210.19(A) Informational Note recommends a maximum 3% voltage drop on branch circuits. If you are running a 12 AWG solid wire 150 feet to a 12A shop vacuum, the wire won't melt, but the voltage at the receptacle will drop below 110V, potentially damaging the motor. For runs over 100 feet, use a voltage drop calculator and upsize the wire by one or two gauges.
  2. Conduit Fill Capacity: Chapter 9 of the NEC limits how much physical space wire can take up inside a conduit (typically 40% for three or more wires). You might have the ampacity to use 14 AWG, but if you are pulling six cables through a 1/2-inch EMT, they physically won't fit without jamming.
  3. Short-Circuit Withstand: The chart assumes standard overcurrent protection. If your service has a high available fault current (e.g., 22,000 amps at the panel), the wire must be able to withstand the magnetic and thermal forces of a short circuit before the breaker trips. This is generally managed by ensuring your breaker's AIC (Amps Interrupting Capacity) rating matches the panel, rather than upsizing the wire.

The Decision Path: Pick Your Exact Wire Size

Stop guessing. Follow this decision tree to select the exact solid copper wire size for standard residential branch circuits. These picks assume standard 60°C/75°C terminations, standard ambient temperatures, and standard NM-B or THHN insulation.

  • IF you are wiring a 15A lighting circuit or general-purpose bedroom/living room receptacles → PICK 14 AWG Solid (NM-B 14/2 or 14/3). Default to 12 AWG if the run exceeds 75 feet to mitigate voltage drop.
  • IF you are wiring a 20A kitchen, bathroom, garage, or outdoor receptacle circuit → PICK 12 AWG Solid (NM-B 12/2). This is the absolute code minimum for these areas.
  • IF you are wiring a 30A electric dryer, RV outlet (TT-30), or heavy-duty window AC → PICK 10 AWG Solid (NM-B 10/2 or 10/3).
  • IF you are wiring a 40A electric range or baseboard heater → PICK 8 AWG Solid (NM-B 8/2 or 8/3). Note: If pulling individual conductors in conduit, you must use 8 AWG Stranded THHN, as solid 8 AWG THHN is virtually unavailable and impossible to pull.
  • IF you are wiring a 50A welder outlet, hot tub, or 60A subpanel feeder → PICK 6 AWG. Use 6/3 NM-B (which may be solid or stranded depending on the manufacturer) for short indoor runs, or 6 AWG Stranded THHN/THWN-2 for conduit runs.
Final Code Caveat: This guide reflects standard NEC-style practice for copper conductors. Local jurisdictions (your local AHJ) may have amendments that restrict 14 AWG entirely, requiring 12 AWG minimum for all branch circuits. Always verify with your local building inspector before rough-in.