The Ultimate Wire Size Ampacity Chart: NEC Table 310.16 Explained

The standard wire size ampacity chart for US residential and commercial wiring is based on NEC Table 310.16 (formerly 310.15(B)(16)). For the most common household branch circuits using copper wire, the baseline rules are straightforward: 14 AWG is rated for 15 amps, 12 AWG for 20 amps, and 10 AWG for 30 amps. However, picking the right wire requires understanding which temperature column applies to your specific insulation and terminals, and how bundling or ambient heat derates those baseline numbers.

How to Read the Wire Size Ampacity Chart

Before scrolling to the full data table, here is how to read it. The chart is divided by conductor material (Copper vs. Aluminum) and then by temperature rating (60°C, 75°C, and 90°C). The temperature rating corresponds to the insulation type stamped on the wire jacket (e.g., TW is 60°C, THHW/THWN is 75°C, THHN/XHHW-2 is 90°C).

Below is the complete allowable ampacity table for copper and aluminum conductors rated 0 through 2000 volts.

Source Standard: NFPA 70 (National Electrical Code) Table 310.16. Allowable Ampacities of Insulated Conductors Rated Up to and Including 2000 Volts in Raceway or Cable.

AWG / kcmil	Copper 60°C (140°F)	Copper 75°C (167°F)	Copper 90°C (194°F)	Aluminum 60°C (140°F)	Aluminum 75°C (167°F)	Aluminum 90°C (194°F)
14*	15	20*	25	-	-	-
12*	20	25*	30	15	20*	25
10*	30	35*	40	25	30*	35
8	40	50	55	30	40	45
6	55	65	75	40	50	60
4	70	85	95	55	65	75
3	85	100	110	65	75	85
2	95	115	130	75	90	100
1	110	130	145	85	100	115
1/0	125	150	170	100	120	135
2/0	145	175	195	115	135	150
3/0	165	200	225	130	155	175
4/0	195	230	260	150	180	205

*Crucial Code Caveat: Per NEC 240.4(D), the overcurrent protection for small conductors is strictly capped. Even though 12 AWG copper has a 75°C ampacity of 25A, you cannot put it on a 25A breaker. 14 AWG is hard-capped at 15A, 12 AWG at 20A, and 10 AWG at 30A, regardless of the higher values in the 75°C or 90°C columns.

Which Temperature Column Applies to Your Installation

The most common mistake DIYers and junior electricians make is looking at the 90°C column because they bought THHN wire, and assuming they can push more current through it. You cannot. The allowable ampacity is dictated by the weakest link in the circuit, governed by NEC 110.14(C).

Here is the practical decision framework for selecting your column:

• Use the 60°C Column When: You are running NM-B (Romex) cable. Even though the individual wires inside NM-B might have 90°C insulation, the NEC mandates that the ampacity of NM-B must be based on the 60°C column. You also use this column if your breaker or terminal lugs are only rated for 60°C (common in older panels or very cheap modern breakers).
• Use the 75°C Column When: You are pulling individual THHN/THWN-2 conductors in conduit, and your breaker terminals and panel lugs are rated for 75°C (which is the standard for almost all modern residential breakers rated 100A or less, and nearly all commercial equipment).
• Use the 90°C Column When: You are calculating derating adjustments (explained below). The 90°C column is your starting baseline for math, but your final adjusted ampacity cannot exceed the 60°C or 75°C limits of your terminations.

Derating and What the Chart Cannot Tell You

The wire size ampacity chart assumes ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together in a raceway. When real-world conditions deviate, you must apply derating factors.

How Derating Modifies the Base Value

When you bundle 4 to 6 current-carrying conductors in a single conduit, the heat generated by the wires cannot dissipate efficiently. Per NEC 310.15(C)(1), you must multiply the base ampacity by 80%.

Worked Example: You are pulling four 10 AWG THHN wires (two hots, one neutral, one ground) through a conduit for a multi-wire branch circuit.
1. Start with the 90°C column for THHN: 10 AWG = 40A.
2. Apply the 80% derating factor for 4 conductors: 40A × 0.80 = 32A.
3. Check termination limits: Your breaker is rated 75°C, and 10 AWG in the 75°C column is 35A.
4. Result: 32A is less than 35A, so the wire is safe. You can protect this circuit with a standard 30A breaker.

What the Table Cannot Tell You: Voltage Drop

The ampacity chart only tells you what size wire will prevent the insulation from melting and starting a fire. It does not account for voltage drop over distance. If you run 14 AWG copper on a 15A circuit for 150 feet, the wire won't overheat, but the voltage at the receptacle will drop below 114V, causing motors to stall and electronics to brown out.

While the NEC mostly treats voltage drop as an informational recommendation (NEC 210.19(A)(Informational Note No. 4)), standard engineering practice limits branch circuit voltage drop to 3%. For a 120V, 15A circuit, if your one-way run exceeds 50 feet, you should upsize from 14 AWG to 12 AWG. If it exceeds 80 feet, upsize to 10 AWG. Always calculate voltage drop for feeder runs over 100 feet.