Amperage to Wire Gauge Chart: Exact AWG Sizing for Home Circuits

For a standard 15A circuit, use 14 AWG copper. For a 20A circuit, use 12 AWG. For a 30A circuit, use 10 AWG. If you are pulling individual THHN wires through conduit rather than running bundled NM-B (Romex) cable, you can sometimes use the 75°C ampacity column to downsize your wire on larger feeds, but for 99% of residential branch circuits, the 60°C column dictates your breaker pairing.

How to Read This Amperage to Wire Gauge Chart

The most common mistake DIYers make when looking up wire ampacity is reading the wrong temperature column. The National Electrical Code (NEC) publishes ampacity tables with three distinct temperature ratings: 60°C, 75°C, and 90°C. Here is how to determine which column applies to your installation:

• 60°C Column: Use this for non-metallic sheathed cable (NM-B, commonly known as Romex) and any circuit rated 100 amps or less where the termination temperature of the breaker or device is unmarked. Per NEC 110.14(C), most standard residential breakers and receptacles are rated for 60°C or 75°C terminations, making the 60°C column the mandatory baseline for NM-B cable.
• 75°C Column: Use this when pulling individual THHN/THWN-2 wires through conduit (EMT, PVC) and terminating on equipment explicitly rated for 75°C (most modern subpanels, large breakers, and heavy-duty receptacles).
• 90°C Column: You can almost never use this column to determine your final breaker size. The 90°C rating of modern THHN wire is used exclusively as a starting point for calculating derating adjustments (like bundling or high ambient heat). Once derated, the final ampacity must still meet the termination limits of the 60°C or 75°C column.

Complete Copper Ampacity Reference (NEC Table 310.16)

The following spec-sheet-table is derived directly from NEC Table 310.16 for copper conductors in an ambient temperature of 30°C (86°F). It covers the sizes most frequently used in residential wiring.

Source: Adapted from NEC Table 310.16 (Copper, 30°C Ambient). Always verify with the latest adopted code cycle in your municipality. For manufacturer-specific insulation ratings, refer to Cerrowire Building Wire specifications.

Quick-Jump Sizing for Common Household Circuits

Bookmark this section for fast lookups on standard residential jobs. These assume standard 120V/240V residential split-phase power and copper conductors.

• 15A Lighting & General Receptacles: 14 AWG NM-B. (Minimum 14 AWG; 12 AWG is acceptable and often preferred by pros to reduce voltage drop and allow future upgrades).
• 20A Kitchen, Bath, Laundry & Garage: 12 AWG NM-B. (NEC requires 20A small-appliance and laundry circuits).
• 30A Electric Dryer or Window AC: 10 AWG NM-B or 10 AWG THHN in conduit.
• 40A Electric Range or Level 2 EV Charger: 8 AWG THHN in conduit. (Note: 8 AWG NM-B is only rated for 40A, but pulling 8 AWG THHN allows you to utilize the 75°C column for a full 50A if your equipment demands it).
• 50A Hot Tub, Welder, or Subpanel Feed: 6 AWG THHN in conduit.
• 100A Subpanel Feed: 3 AWG THHN (copper) or 1 AWG Aluminum (XHHW).

Derating Factors: When Your Base Ampacity Drops

The ampacity table above assumes you have no more than three current-carrying conductors in a raceway and an ambient temperature below 30°C (86°F). When conditions change, you must apply derating multipliers to the 90°C column, then verify the result against your termination temperature limits.

Decision Tree: Picking Your Exact Wire and Breaker

Use this logical path to terminate your decision-making and pick your materials from the hardware store shelf.

• IF you are running cable inside standard drywall cavities without conduit → THEN buy NM-B (Romex) and size strictly using the 60°C column.
• IF you are pulling individual wires through PVC or EMT conduit to a subpanel or heavy appliance → THEN buy THHN/THWN-2 and size using the 75°C column (checking the 90°C column only if derating is required).
• IF your calculated load is exactly on the boundary of a wire size (e.g., a 24A continuous load on a 30A circuit) → THEN upsize to the next wire gauge to prevent nuisance tripping and voltage sag.
• IF you are wiring standard 120V, 20A general-purpose receptacles in a living room → THEN execute the default pick below.

What This Amperage to Wire Gauge Chart Cannot Tell You

While NEC Table 310.16 is the bible for thermal limits, it does not account for physics that occur over long distances or with different materials. Keep these blind spots in mind:

1. Voltage Drop: Ampacity only tells you what the wire can handle before the insulation melts. It does not guarantee the voltage will reach the load. For any circuit run exceeding 100 feet, you must calculate voltage drop. A 3% drop is the accepted maximum for branch circuits. A 12 AWG wire on a 20A breaker spanning 150 feet will drop nearly 5% of your voltage; you must upsize to 10 AWG or 8 AWG to compensate, even though the breaker is only 20A.
2. Aluminum vs. Copper: This chart is strictly for copper. If you are using aluminum wire (common for heavy feeder lines to subpanels due to cost), aluminum has lower conductivity. You must generally upsize aluminum by two AWG steps compared to copper to achieve the same ampacity (e.g., use 2 AWG Aluminum where you would use 4 AWG Copper).
3. Conduit Fill Capacity: Just because the ampacity chart says 10 AWG is fine doesn't mean you can physically fit twelve 10 AWG wires into a half-inch EMT conduit. You must cross-reference NEC Chapter 9, Table 1 to ensure your conduit isn't overfilled, which traps heat and invalidates the ampacity chart entirely.
4. Continuous vs. Non-Continuous Loads: If a load will run for 3 hours or more (like an EV charger or space heater), the NEC requires you to multiply the load by 125%. A 16A continuous load requires a circuit rated for 20A (16 × 1.25 = 20A), meaning you must use 12 AWG wire and a 20A breaker, not 14 AWG.