For standard residential branch circuits, the baseline rule is simple: 15A uses 14 AWG, 20A uses 12 AWG, and 30A uses 10 AWG copper wire. However, once you move beyond standard receptacles into appliance circuits, subpanel feeders, or service entrances, guessing leads to tripped breakers, melted lugs, or failed inspections. To size conductors correctly, you must use the National Electrical Code (NEC) Table 310.16. This guide provides the complete amp to wire size chart, explains exactly which temperature column applies to your installation, and gives you a concrete decision path to pick the right gauge every time.

How to Read This Amp to Wire Size Chart

Before looking at the numbers, you must understand the temperature columns. Wire insulation (like THHN or XHHW) is rated for high temperatures (90°C), but the terminations at your breakers and lugs are usually rated lower. NEC 110.14(C)(1)(a) dictates how to reconcile this:

  • 60°C Column: The mandatory default for circuits rated 100A or less, or for conductors sized 14 AWG through 1 AWG. Even if your wire is 90°C THHN, you must use the 60°C ampacity for your final breaker sizing unless the equipment is explicitly marked otherwise.
  • 75°C Column: The default for circuits rated over 100A, or conductors larger than 1 AWG. Most modern commercial lugs and heavy residential breakers are rated for 75°C.
  • 90°C Column: Never use this column for final ampacity sizing. It is used exclusively as the starting point for calculating derating adjustments (like bundling wires in a hot attic). The final derated value is then capped by the 60°C or 75°C base ampacity.

NEC Table 310.16: Amp to Wire Size Chart (Copper & Aluminum)

The following table is derived from the NFPA 70 National Electrical Code (NEC) Table 310.16. It assumes an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway. For authoritative guidance on conductor properties, refer to the Copper Development Association.

Bookmark Quick-Jumps: The most queried residential sizes are highlighted in bold below. For 15A, look at 14 AWG Cu (60°C). For 20A, look at 12 AWG Cu (60°C). For 200A service entrances, look at 4/0 AWG Al (75°C).
Wire Size (AWG/kcmil) Copper 60°C Copper 75°C Copper 90°C Aluminum 75°C Aluminum 90°C
14 AWG15A20A25A——
12 AWG20A25A30A15A—
10 AWG30A35A40A30A35A
8 AWG40A50A55A40A45A
6 AWG55A65A75A50A55A
4 AWG70A85A95A65A75A
3 AWG85A100A115A75A85A
2 AWG95A115A130A90A100A
1 AWG110A130A145A100A115A
1/0 AWG125A150A170A120A135A
2/0 AWG145A175A195A135A150A
3/0 AWG165A200A225A155A175A
4/0 AWG195A230A260A180A205A

Decision Path: Picking Your Exact Wire Gauge

Stop guessing and follow this decision tree to land on the exact conductor material and size for your project.

If your installation is... Then choose this Material & Column... Concrete Example & Pick
A standard 120V/240V branch circuit (lighting, receptacles) under 50A. Copper (NM-B or THHN), 60°C column. 20A kitchen circuit = 12 AWG Copper.
A heavy appliance (electric range, EV charger, dryer) between 50A and 100A. Copper or Aluminum, 60°C column (unless lugs are stamped 75°C). 50A EV charger = 6 AWG Copper (55A base) or 4 AWG Aluminum.
A subpanel feeder or main service entrance over 100A. Aluminum (for cost savings), 75°C column. 200A residential service = 4/0 AWG Aluminum.

The Default Recommendation: If you are wiring a standard home branch circuit and are unsure about the breaker terminal ratings, default to Copper wire sized from the 60°C column. It is universally accepted by every inspector and guarantees compliance with NEC 110.14.

Derating Factors: When Base Ampacity Drops

The chart above assumes perfect conditions: 30°C ambient temperature and no more than three current-carrying conductors (CCCs) in a single conduit. When real-world conditions worsen, you must apply derating factors from NEC 310.15.

How derating modifies the base value:
You calculate derating using the 90°C column, not the 60°C column. However, the final calculated ampacity cannot exceed the base ampacity of the 60°C or 75°C column for that wire size.

Worked Example: Bundling in Conduit
You are pulling 4 current-carrying conductors through a single EMT conduit for a 30A circuit. NEC Table 310.15(C)(1) requires an 80% adjustment factor for 4-6 CCCs.
Step 1: Look at 10 AWG THHN in the 90°C column = 40A.
Step 2: Apply derating: 40A × 0.80 = 32A.
Step 3: Check the cap. The 60°C base ampacity for 10 AWG is 30A. Because 32A > 30A, the wire is capped at 30A. Result: 10 AWG is still legal for a 30A breaker.

But what if you had 10 CCCs (50% derating)?
40A × 0.50 = 20A. A 20A derated capacity is not enough for a 30A breaker. You must upsize to 8 AWG THHN (90°C = 55A; 55A × 0.50 = 27.5A, which still fails the 60°C cap of 40A, wait—8 AWG 60°C cap is 40A, so 27.5A is the final limit. You'd actually need 6 AWG THHN to maintain 30A after a 50% derating). This is why bundling forces larger wire.

What This Chart Cannot Tell You

While NEC Table 310.16 is the ultimate authority on thermal ampacity (preventing the wire from melting or degrading its insulation), it is blind to several critical physical and electrical realities. Before finalizing your wire size, verify these three constraints:

  1. Voltage Drop: The NEC does not strictly mandate voltage drop limits for branch circuits (it's an informational note, not an enforceable article in most jurisdictions), but exceeding a 3% drop on branch circuits or 5% on feeders will cause motors to overheat and electronics to brownout. If your run exceeds 100 feet, use a voltage drop calculator. You will likely need to upsize your wire by one or two AWG steps beyond what this chart dictates.
  2. Conduit Fill Capacity: NEC Chapter 9, Table 1 limits conduit fill to 40% for three or more wires. You might electrically need three 4/0 AWG aluminum conductors for a 200A feeder, but physically, they will not fit into a 1.5-inch PVC conduit. You must check the physical cross-sectional area against your conduit size.
  3. Local AHJ Amendments and Fault Current: This chart assumes standard residential fault currents. In industrial settings with high available short-circuit current, the magnetic forces and let-through energy can destroy undersized conductors before the breaker trips. Furthermore, your local Authority Having Jurisdiction (AHJ) may have amended the NEC to require larger minimums (e.g., banning 14 AWG entirely and requiring 12 AWG minimum for all branch circuits). Always defer to your local inspector's final authority.