When sizing conductors for branch circuits, feeders, or subpanels, guessing is not an option. The foundational reference for North American wire sizing is NEC Table 310.16 (formerly 310.15(B)(16)). This wire gage chart provides the allowable ampacities for insulated conductors rated up to 2000 volts, based on conductor material, size (AWG/kcmil), and temperature rating.

How to read this table: The rows represent the American Wire Gage (AWG) size. The columns are split by conductor material (Copper vs. Aluminum/Copper-Clad) and insulation temperature rating (60°C, 75°C, 90°C). Always read the table assuming an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a raceway. If your installation differs, you must apply derating factors to the 90°C column before finalizing your size.

The Master Wire Gage Chart (NEC Table 310.16)

The following data is extracted directly from the National Electrical Code. Bookmark this section for quick jobsite lookups. Source standard: NFPA 70 (NEC) Table 310.16.

Allowable Ampacities for Copper and Aluminum Conductors (Ambient 30°C)
AWG Size Copper 60°C Copper 75°C Copper 90°C Aluminum 60°C Aluminum 75°C Aluminum 90°C
14 AWG*15A20A25A---
12 AWG*20A25A30A---
10 AWG*30A35A40A---
8 AWG40A50A55A30A40A45A
6 AWG55A65A75A40A50A60A
4 AWG70A85A95A55A65A75A
3 AWG85A100A115A65A75A85A
2 AWG95A115A130A75A90A100A
1 AWG110A130A145A85A100A115A
1/0 AWG125A150A170A100A120A135A
2/0 AWG145A175A195A115A135A150A
3/0 AWG165A200A225A130A155A175A
4/0 AWG195A230A260A180A205A230A
NEC 240.4(D) Small Conductor Rule: The ampacities for 14, 12, and 10 AWG copper marked with an asterisk (*) are overridden by NEC 240.4(D) for overcurrent protection. Regardless of the 75°C or 90°C column values, 14 AWG is limited to 15A breakers, 12 AWG to 20A, and 10 AWG to 30A in standard residential branch circuits.

Which Column Applies to Your Installation?

The most common mistake DIYers and junior apprentices make is defaulting to the 90°C column because modern wire insulation (like THHN/THWN-2) is rated for it. You cannot use the 90°C column for final circuit ampacity unless the equipment terminations are explicitly rated for 90°C—which is exceptionally rare in residential and light commercial gear.

Here is the decision framework for selecting your column, governed by NEC 110.14(C):

  • The 60°C Column: Use this for circuits rated 100 amps or less, or for conductors sized 14 AWG through 1 AWG. Furthermore, if you are using NM-B (Romex) cable, NEC 334.80 mandates that you must use the 60°C column for ampacity, even though the individual conductors inside the jacket have 90°C insulation.
  • The 75°C Column: Use this for circuits rated over 100 amps, or for conductors sized larger than 1 AWG (e.g., 1/0 to 4/0). Most modern breakers, lugs, and subpanel busbars are stamped with a 75°C rating.
  • The 90°C Column: Use this only as the starting point for calculating derating adjustments (ambient temperature or conductor bundling). After derating, the final allowable ampacity must not exceed the 60°C or 75°C limits of your terminations.

How Derating Rows Modify the Base Value

The base values in the wire gage chart assume an ambient temperature of 86°F (30°C) and no more than three current-carrying conductors (CCCs) in a raceway. When you exceed these parameters, you must apply correction factors found in NEC Table 310.15(B)(1) and Table 310.15(C)(1).

Worked Example: You are pulling four 6 AWG copper THHN wires through a conduit in an attic where the ambient temperature reaches 113°F (45°C). You are feeding a 60A subpanel with 75°C terminations.

  1. Base 90°C Ampacity: The table shows 6 AWG at 90°C is 75A.
  2. Temperature Correction: At 113°F, the 90°C column correction factor is 0.82. (75A × 0.82 = 61.5A).
  3. Bundling Correction: Four CCCs require an 80% derating factor. (61.5A × 0.80 = 49.2A).
  4. Termination Check: Your final derated ampacity is 49.2A. The 75°C column limit for 6 AWG is 65A. Since 49.2A is less than 65A, the 6 AWG wire is legally permitted, but it can only carry 49.2A safely. If your continuous load exceeds 39A (80% of 49.2A), you must upsize to 4 AWG.

What This Wire Gage Chart Cannot Tell You

While NEC Table 310.16 is the bible for thermal limits, it is blind to voltage drop. The chart will tell you that 12 AWG copper can safely carry 20A without melting the insulation, but it will not tell you that pushing 20A through 150 feet of 12 AWG wire will result in a voltage drop of nearly 10 volts on a 120V circuit.

For optimal equipment performance and motor longevity, industry standards (and many local AHJs) recommend keeping voltage drop under 3% for branch circuits and 5% for the total feeder-plus-branch combined. When running long distances to a detached garage, well pump, or EV charger, you must use a voltage drop calculator and upsize your wire beyond what the ampacity chart strictly requires. Additionally, this chart does not account for local code amendments; some municipalities mandate a baseline 12 AWG minimum for all 15A and 20A residential receptacle circuits, effectively eliminating 14 AWG from new construction.

Wire Gage Chart FAQ

What wire gage do I need for a 50 amp breaker?

For a standard 50A circuit (like an EV charger or range) with copper wire and 75°C terminations, you need 6 AWG copper. The 75°C column rates 6 AWG at 65A, which safely covers the 50A breaker. If you are using aluminum wire (like SER cable for a subpanel feeder), you must use 4 AWG aluminum, which is rated for 65A in the 75°C column. Never use 8 AWG copper (rated 50A at 75°C) for a 50A breaker if the load is continuous (running for 3+ hours), as continuous loads must be derated to 80% (requiring a 62.5A capacity).

How do I read a wire gage chart for 12V DC systems?

Standard NEC AC ampacity charts do not directly apply to low-voltage 12V/24V DC systems (like solar or RV wiring) because voltage drop becomes the governing constraint, not thermal melting. At 12V, a mere 1-volt drop is an 8.3% loss. For DC systems, ignore the 60°C/75°C termination columns and size your wire using a DC voltage drop calculator targeting a maximum 2% drop. For example, a 30A solar charge controller located 10 feet from the battery bank requires 8 AWG copper, even though the thermal ampacity chart suggests 10 AWG would suffice.

What is the difference between AWG and SWG on a wire gage chart?

AWG (American Wire Gage) is the standard used in North America for electrical building wire, electronics, and automotive applications. SWG (Standard Wire Gage), also known as Imperial Wire Gage, is an older British standard primarily used for guitar strings, specific craft wires, and legacy telecommunications. They are not interchangeable. For example, 18 AWG is 1.024mm in diameter, while 18 SWG is 1.219mm. Always ensure your wire gage chart explicitly states 'AWG' or 'Brown & Sharpe (B&S)' before sizing electrical conductors.

Does a wire gage chart include the insulation thickness?

No. The AWG designation and the ampacities in NEC Table 310.16 refer strictly to the bare metal conductor. The physical outer diameter of the wire, which you need to calculate conduit fill capacity (NEC Chapter 9, Table 1), includes the insulation. For instance, a 10 AWG THHN conductor has a bare diameter of 0.1019 inches, but its overall diameter with insulation is roughly 0.164 inches. Always consult the manufacturer's spec sheet (like Southwire or Cerro Wire) for exact outer dimensions when calculating how many wires will fit inside EMT or PVC conduit.