If you need the direct answer right now: for a standard residential copper branch circuit, use 14 AWG for 15 amps, 12 AWG for 20 amps, 10 AWG for 30 amps, 8 AWG for 40 amps, and 6 AWG for 50 amps. These sizes align with the 60°C and 75°C ampacity limits defined in the National Electrical Code (NEC). However, simply matching a breaker to a wire gauge without understanding the temperature columns and derating factors is how DIYers melt terminal lugs and fail inspections.

This reference guide provides the complete NEC Table 310.16 ampacity data, explains exactly which temperature column applies to your specific installation, and provides a concrete decision path to lock in your wire size.

How to Read the Amp to Wire Gauge Chart

Before looking at the numbers, you must understand the three temperature columns: 60°C, 75°C, and 90°C. These columns represent the thermal limit of the wire's insulation and the equipment terminations it connects to.

  • The 60°C Column: Mandated by NEC 240.4(D) for small conductors (14, 12, and 10 AWG). Even if your wire insulation is rated for 90°C, you must use the 60°C column to size the overcurrent protection for these small wires. This is why 12 AWG is capped at 20A, despite having a 90°C rating of 30A.
  • The 75°C Column: The standard for most modern residential breakers, lugs, and receptacles. For wires 8 AWG and larger, this is the column you will use 95% of the time to determine your final breaker size.
  • The 90°C Column: Never use this column to size your breaker. The 90°C column is used exclusively as a starting point for calculating derating factors (like bundling wires in a conduit or high ambient temperatures). After derating, you must still terminate based on the 75°C (or 60°C) limits.
Bench Tip: Always check the side of your breaker or receptacle. If it is stamped "CU-AL" or "75°C", you are cleared to use the 75°C column for wires 8 AWG and up. If it has no marking, NEC 110.14(C) forces you to default to the 60°C column.

Complete NEC Table 310.16 Ampacity Chart

The following table is sourced directly from NEC Table 310.16 (formerly 310.15(B)(16)). It assumes an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway or cable. Bookmark this section for quick lookups on the most common residential sizes.

AWG / kcmil Copper 60°C (140°F) Copper 75°C (167°F) Copper 90°C (194°F) Aluminum 75°C (167°F)
14 AWG15A—25A—
12 AWG20A—30A—
10 AWG30A35A40A—
8 AWG40A50A55A40A
6 AWG55A65A75A50A
4 AWG70A85A95A65A
3 AWG85A100A115A75A
2 AWG95A115A130A90A
1 AWG110A130A145A100A
1/0 AWG125A150A170A120A
2/0 AWG145A175A195A135A
3/0 AWG165A200A225A155A
4/0 AWG195A230A260A180A

Decision Path: Sizing Your Branch Circuit Wire

Use this decision-tree-table to lock in your exact wire gauge and breaker pairing. Follow the rows from top to bottom based on your specific load.

If Your Load / Appliance Is... Then Pick This Breaker... And Buy This Copper Wire... Governing NEC Rule
General lighting / standard 120V receptacles 15A or 20A 14 AWG (15A) or 12 AWG (20A) 240.4(D)
Small appliance kitchen / bathroom GFCI circuits 20A 12 AWG NM-B or THHN 210.11(C)(1)
Standard electric dryer (30A receptacle) 30A 10 AWG (3-wire + ground) 240.4 / 240.4(D)
Electric range / oven (up to 40A draw) 40A or 50A 8 AWG (40A) or 6 AWG (50A) 210.19 / 240.4(B)
Subpanel feeder (up to 60A continuous) 60A 6 AWG Copper or 4 AWG Aluminum 215.2 / 310.16
Main service entrance / large subpanel (100A) 100A 3 AWG Copper or 1 AWG Aluminum 230.42 / 310.16
Default Recommendation: If you are wiring a standard 120/240V residential branch circuit under 100A and are unsure about termination ratings, default to copper THHN/THWN-2 and size strictly to the 75°C column. It provides the best balance of physical flexibility, terminal compatibility, and cost. Avoid aluminum for branch circuits under 50A due to termination torque sensitivities and oxidation risks in standard residential receptacles.

How Derating Modifies Your Base Ampacity

The numbers in the chart above assume ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a single conduit. When you deviate from this, you must apply derating factors. Here is how derating actually works in practice.

Step 1: Start with the 90°C column. Let's say you are pulling five current-carrying conductors (e.g., two 3-way switch loops and a neutral) through a single 3/4" EMT conduit in an attic where the ambient temperature hits 40°C (104°F). You are sizing for a 30A load. You start with 10 AWG THHN, which has a 90°C base ampacity of 40A.

Step 2: Apply the bundling derating. NEC Table 310.15(C)(1) states that 4 to 6 current-carrying conductors require an 80% adjustment factor.
Calculation: 40A × 0.80 = 32A.

Step 3: Apply the ambient temperature correction. NEC Table 310.15(B)(1) for 90°C insulation at 40°C ambient gives a correction factor of 0.91.
Calculation: 32A × 0.91 = 29.12A.

Step 4: Check the termination limits. Your calculated derated ampacity is 29.12A. Because your breaker terminations are rated for 75°C, you must look at the 75°C column for 10 AWG, which is 35A. Since 29.12A is less than 35A, and less than the 30A breaker trip rating, 10 AWG THHN is legally and safely compliant for this run. If the final number had dropped below your breaker size, you would be forced to step up to 8 AWG.

What This Chart Cannot Tell You

While NEC Table 310.16 is the bible for thermal ampacity, it is blind to three critical physical realities that will ruin your installation if ignored.

  1. Voltage Drop Over Distance: Ampacity only tells you what the wire can handle before the insulation melts. It does not tell you if the voltage at the end of a 150-foot run to a detached garage will drop below the 3% threshold recommended by the Copper Development Association. For a 50A EV charger located 150 feet from the panel, 6 AWG copper is thermally safe, but it will suffer a ~5.5% voltage drop. You must upsize to 4 AWG or 3 AWG purely to maintain voltage stability.
  2. Physical Lug Sizing: A standard 100A residential subpanel usually has lugs rated to accept a maximum of #1 or #2 AWG wire. If your voltage drop calculation requires you to run 1/0 AWG feeder wire, you cannot physically fit it into the panel lugs. You will need to install a Polaris splice block or lug reducer inside the panel to step down to a short pigtail of #2 AWG.
  3. Continuous vs. Non-Continuous Loads: The chart assumes standard breaker sizing. If your load runs for 3 hours or more continuously (like an EV charger or baseboard heaters), NEC 210.20(A) requires you to size the breaker at 125% of the continuous load. A 32A continuous EV charger requires a 40A breaker (32 × 1.25 = 40), which in turn mandates 8 AWG wire, not the 10 AWG you might initially guess for a 32A draw.

Always pair this amp to wire gauge chart with a voltage drop calculator for runs exceeding 50 feet, and verify the physical lug ratings on your specific breaker and panelboard before purchasing bulk wire.