AWG and Amperage Sizing Chart: NEC Table 310.16 Explained

If you need the direct answer for standard residential branch circuits using copper NM-B (Romex) cable: use 14 AWG for 15A, 12 AWG for 20A, 10 AWG for 30A, and 6 AWG for 50A. These values are pulled directly from the 60°C column of the National Electrical Code (NEC) ampacity tables. However, picking the right wire for a subpanel feeder, a long underground run, or a high-heat attic requires understanding exactly how the NEC calculates ampacity. This reference guide breaks down the master NEC Table 310.16, explains which temperature column legally applies to your terminations, and provides a concrete decision path for your next pull.

The Master AWG and Amperage Chart (NEC Table 310.16)

The table below is the foundational reference for copper conductor ampacity in North America. It is derived directly from NEC Table 310.16 for 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 or cable.

Bookmark Quick-Jumps for Common Circuits

• 15A Lighting/Receptacles: 14 AWG (60°C column)
• 20A Kitchen/Bath/Garage: 12 AWG (60°C column)
• 30A Dryer/Water Heater/RV: 10 AWG (60°C column)
• 50A Range/Hot Tub Subpanel: 6 AWG (60°C column for NM-B) or 8 AWG (75°C column for THHN in conduit)

Which Temperature Column Actually Applies to Your Wire?

A common bench and jobsite mistake is looking at a spool of 12 AWG THHN, seeing '30A' in the 90°C column, and assuming it can be protected by a 30A breaker. This is a code violation and a fire hazard.

NEC Section 110.14(C) dictates that the ampacity of a circuit is limited by the lowest temperature rating of any connected component, including the breaker lugs, receptacles, and splices. Here is the hard rule for selecting your column:

• Circuits 100A or less: You must use the 60°C column unless the equipment is explicitly marked for 75°C terminations. Most standard residential breakers and receptacles are rated 60°C/75°C, but standard NM-B (Romex) cable is strictly limited to the 60°C column by NEC 334.80, regardless of the THHN insulation on the individual wires inside the jacket.
• Circuits over 100A: You must use the 75°C column unless the equipment is marked otherwise.
• The 90°C Column: This column is almost never used for final ampacity. It is used exclusively as the starting point for derating calculations before you apply the termination temperature cap.

Derating: When Your Base Ampacity Drops

The numbers in the master table assume a perfect environment: 30°C (86°F) ambient air and no more than three current-carrying conductors bundled together. When reality deviates from this, you must derate the wire using the 90°C column as your baseline math, then compare the result to your termination column limit. The final legal ampacity is the lower of the two numbers.

Adjustment Factor 1: Bundling (More than 3 Current-Carrying Conductors)

If you pull four or more current-carrying conductors through a single conduit, the wires heat each other up. Per NEC Table 310.15(C)(1), 4 to 6 conductors require an 80% adjustment factor.

Worked Example: You are pulling four 10 AWG THHN wires in a conduit for two 20A circuits (two hots, two neutrals).
1. Base 90°C ampacity for 10 AWG = 40A.
2. Bundling derate (80%): 40A × 0.80 = 32A.
3. Termination limit (60°C column for standard breakers) = 30A.
Result: The final ampacity is 30A. You must protect this wire with a maximum 30A breaker, meaning you cannot use it for two 20A circuits. You must upsize to 8 AWG THHN.

Adjustment Factor 2: Ambient Temperature

If your conduit runs across an attic where the ambient temperature hits 50°C (122°F), you must apply the ambient temperature correction factor from NEC Table 310.15(B)(1). For 90°C wire at 50°C ambient, the multiplier is 0.82. Multiply your 90°C base ampacity by 0.82, then check against your termination limit.

What the Ampacity Table Cannot Tell You

NEC Table 310.16 tells you the thermal limit of the wire insulation, but it is blind to three critical physical realities of your installation:

1. Voltage Drop: The NEC ampacity tables do not account for distance. A 12 AWG wire is legally rated for 20A at 200 feet, but at that distance on a 120V circuit, you will experience a 6.4% voltage drop (NEC recommends keeping it under 3%). For long runs, you must upsize the wire purely for voltage drop, even if the ampacity table says the smaller wire is thermally safe. Use the formula: VD = (2 × K × I × D) / CM (where K=12.9 for copper, I=amps, D=distance, CM=circular mils).
2. Conduit Fill Capacity: The table assumes the wires fit in the pipe. NEC Chapter 9, Table 1 limits conduit fill to 40% for three or more wires. You cannot legally stuff six 6 AWG THHN wires into a 1/2-inch EMT conduit, regardless of their ampacity.
3. Physical Lug Sizing: A 2/0 AWG wire might be required for a 200A residential service, but if you are feeding a specific HVAC disconnect or a subpanel lug that is only physically rated to accept up to 1/0 AWG, you cannot jam the larger wire in. You must use a mechanical lug reducer or a panel with larger termination blocks.

Decision Tree: Pick Your Exact Wire and Breaker Size

Stop guessing. Use this decision matrix to lock in your exact materials for standard copper installations. This path terminates in a concrete pick based on NEC-style guidance; always verify with your local AHJ (Authority Having Jurisdiction) as local amendments can override baseline NEC rules.