The Ultimate Wire Gauge AWG Chart: Sizing, Ampacity, and NEC Rules

For standard residential branch circuits, the baseline rule is simple: use 14 AWG for 15A, 12 AWG for 20A, and 10 AWG for 30A. However, once you move beyond standard receptacles into large appliances, subpanel feeders, or EV chargers, guessing wire size leads to melted terminations or tripped breakers. To size larger conductors correctly, you must use the wire gauge AWG chart codified in NEC Table 310.16, apply the correct temperature column, and adjust for real-world installation conditions.

How to Read the NEC Wire Gauge AWG Chart

The National Electrical Code (NEC) does not assign a single ampacity to a wire size. Instead, ampacity is determined by the thermal limits of the wire's insulation. The chart is divided into three primary temperature columns for copper: 60°C (140°F), 75°C (167°F), and 90°C (194°F).

To read the table correctly, locate your wire gauge (AWG or kcmil) in the leftmost column, then read across to the temperature rating that matches your installation's limiting factor. The most common mistake DIYers make is looking at the 90°C column because they purchased THHN wire (which is rated for 90°C) and assuming they can use that higher ampacity. As we will cover below, the wire's insulation rating is only half the equation; the termination rating of your breaker or lug is the other half.

The Complete Copper Ampacity Reference (NEC Table 310.16)

The following table reproduces the allowable ampacities for insulated copper conductors rated up to 2000 volts, assuming an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway. Bookmark this section for quick jobsite lookups.

*Note: NEC 240.4(B) allows the next standard breaker size up if the calculated load does not match a standard breaker rating, provided the wire ampacity is not exceeded.

Which Temperature Column Applies to Your Installation

This is where the NEC 110.14(C) terminal temperature limitations rule dictates your choice. You must use the lowest temperature rating of any connected device, termination, or conductor in the circuit.

Concrete Example: You are wiring a 60A EV charger using THHN wire in conduit. THHN is rated 90°C. However, the breaker lugs are rated 75°C, and the circuit is under 100A. If you use NM-B cable, you are locked to the 60°C column, meaning 6 AWG is rated for only 55A (requiring you to upsize to 4 AWG). If you use THHN in conduit with 75°C rated terminations, you can use the 75°C column, where 6 AWG is rated for 65A, safely allowing a 60A breaker.

Derating: When the Base Chart Values Change

The ampacity table assumes ideal conditions: an ambient temperature of 30°C (86°F) and a maximum of three current-carrying conductors bundled together. When reality deviates from this baseline, you must apply derating factors (NEC 310.15).

Ambient Temperature Derating

If your conduit runs through a hot attic or outdoors in a desert climate, the wire cannot dissipate heat as efficiently. For example, if the ambient temperature is 46-50°C (115-122°F), you must multiply the 90°C column ampacity by 0.82.

Bundling Derating (More than 3 Conductors)

When you pull four or more current-carrying conductors through a single conduit, they heat each other up.
The Math: You are pulling four 12 AWG THHN wires (two hots, one neutral, one ground) through a conduit to feed a multi-wire branch circuit.
• Base 90°C ampacity for 12 AWG = 30A.
• NEC Table 310.15(C)(1) derating factor for 4-6 conductors = 80%.
• 30A × 0.80 = 24A adjusted ampacity.
Because 24A is still above your 20A breaker, the 12 AWG wire is legally compliant. If you added a fifth circuit (10 current-carrying conductors), the derating drops to 50% (15A), forcing you to upsize to 10 AWG.

Voltage Drop: What the Ampacity Table Cannot Tell You

The wire gauge AWG chart only tells you the maximum current a wire can carry before its insulation melts. It tells you absolutely nothing about voltage drop over distance. If you run 6 AWG copper 150 feet to a 50A RV receptacle, the wire will not catch fire, but the voltage at the receptacle will sag below 215V, potentially damaging the RV's air conditioner compressor.

Industry best practice (and NEC informational note 210.19(A)) recommends keeping voltage drop under 3% for branch circuits and 5% for the total feeder plus branch. Always run long runs through a dedicated voltage drop calculator. As a rough rule of thumb for 240V circuits: upsize your wire by one AWG step for every 100 feet of run beyond 50 feet.

Decision Tree: Match Your Load to the Exact Wire and Breaker

Use this decision matrix to terminate your planning phase and pick your exact materials. This assumes standard residential copper wiring, NM-B (Romex) or THHN in conduit, and standard ambient temperatures.