For standard residential branch circuits, the baseline rule is simple: use the 60°C ampacity column for NM-B (Romex) cable and the 75°C column for THHN wire in conduit. A 14 AWG wire handles 15 amps, 12 AWG handles 20 amps, and 10 AWG handles 30 amps. However, picking the right wire goes beyond memorizing three basic numbers. You must account for insulation temperature ratings, continuous loads, and conduit fill derating.

This reference guide provides the complete electric wire chart for copper conductors based on the National Electrical Code (NEC), along with a concrete decision path to select your exact wire gauge and breaker size.

How to Read This Electric Wire Chart

The ampacity values below are sourced directly from NFPA 70 (NEC) Table 310.16. Before picking a row, you must understand which temperature column applies to your specific installation.

The Temperature Column Rule:
  • 60°C (140°F) Column: Use this for NM-B (Romex) cable, UF-B cable, and any wire connected to terminals rated for 60°C. Even if your NM-B wire has 90°C insulation, the NEC limits its ampacity to the 60°C column.
  • 75°C (167°F) Column: Use this for THHN/THWN-2 wires pulled through conduit. Most modern breakers and lugs are rated for 75°C, making this the standard column for conduit runs.
  • 90°C (194°F) Column: This column is almost never used for final ampacity. It is only used as the starting baseline for calculating derating adjustments (explained below).

The Master Electric Wire Chart (NEC Table 310.16)

This table covers the most frequently used copper wire sizes for residential and light commercial work. Use the quick-jump links to skip to the most queried sizes.

Quick Jump: 14 AWG | 12 AWG | 10 AWG | 8 AWG | 6 AWG | 4 AWG | 2 AWG

AWG Size 60°C Ampacity (NM-B) 75°C Ampacity (THHN) Standard Max Breaker Common Application
14 AWG 15A 20A 15A General lighting, 120V receptacles
12 AWG 20A 25A 20A Kitchen/bath receptacles, 240V baseboard heaters
10 AWG 30A 35A 30A Dryers, 240V water heaters, A/C disconnects
8 AWG 40A 50A 40A (or 50A for THHN) Cooktops, subpanel feeders (short runs)
6 AWG 55A 65A 60A Electric ranges, 60A subpanel feeders
4 AWG 70A 85A 80A 100A subpanel feeders (with 75°C terminations)
3 AWG 85A 100A 100A 100A subpanel feeders
2 AWG 95A 115A 100A (or 125A) 125A subpanel feeders, heavy EV chargers
1 AWG 110A 130A 125A Large subpanels
1/0 AWG 125A 150A 150A 150A service entrance
2/0 AWG 145A 175A 175A 200A service entrance (short runs)
3/0 AWG 165A 200A 200A 200A service entrance (standard)
4/0 AWG 195A 230A 225A 200A+ service entrance, long runs

Derating: When Your Base Ampacity Drops

The ampacity numbers in the chart above assume ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together in a single raceway. When you deviate from these conditions, you must apply derating factors as outlined in NEC ampacity adjustment guidelines.

Derating is calculated using the 90°C column baseline, not the 60°C or 75°C final limits. Here is how it works in practice:

Worked Example: Bundled Wires in Conduit
You are pulling four current-carrying 12 AWG THHN wires through a single EMT conduit to feed two separate 20A circuits.
  • Step 1: Find the 90°C baseline for 12 AWG THHN (30A).
  • Step 2: Apply the bundling derating factor. For 4 to 6 current-carrying conductors, the NEC mandates an 80% adjustment factor.
  • Step 3: Multiply: 30A × 0.80 = 24A.
  • Step 4: Compare to the termination limit. The 75°C termination limit for 12 AWG is 25A. Since 24A is less than 25A, your derated ampacity is 24A.
  • Result: 24A is still greater than your 20A breaker size. The 12 AWG wire is legally safe to use.

If you were pulling 9 current-carrying conductors, the derating factor drops to 70%. That same 12 AWG wire would derate to 21A (30A × 0.70), which is still acceptable for a 20A breaker, but leaves almost no margin for error or ambient heat.

Decision Path: Picking the Exact Wire and Breaker

Use this decision tree to lock in your exact materials for common DIY and residential projects. This path assumes copper wire and standard 120V/240V split-phase power.

Scenario Load Calculation Wire Selection Breaker Selection
Standard 120V Bedroom Receptacles Non-continuous, general use (under 15A total). 14 AWG NM-B (or 12 AWG for future-proofing). 15A (Single-pole, AFCI).
Kitchen Small-Appliance Circuit Non-continuous, but high surge potential (toasters, mixers). 12 AWG NM-B. Never use 14 AWG here. 20A (Single-pole, GFCI/AFCI).
240V Baseboard Heater (1500W) 1500W ÷ 240V = 6.25A. Continuous load (× 1.25) = 7.8A. 14 AWG THHN in conduit (or 14/2 NM-B). 15A (Double-pole).
Electric Water Heater (4500W) 4500W ÷ 240V = 18.75A. Continuous load (× 1.25) = 23.4A. 10 AWG NM-B or THHN. 30A (Double-pole).
Level 2 EV Charger (48A continuous) 48A × 1.25 = 60A minimum circuit ampacity. 4 AWG THHN (85A at 75°C, allows headroom). 60A (Double-pole, hardwired).

What This Chart Cannot Tell You

An ampacity chart dictates the maximum current a wire can carry before its insulation melts or degrades. It does not account for voltage drop, physical installation limitations, or local code amendments.

1. Voltage Drop

The NEC recommends keeping voltage drop under 3% for branch circuits and 5% total from the service entrance to the furthest outlet. If you are running a 120V circuit to a detached garage 150 feet away, a 14 AWG wire carrying 12A will experience a voltage drop of roughly 6%. Your tools will run hot and lights will dim. For runs over 100 feet, always step up one or two AWG sizes from the chart minimums to compensate for resistance over distance.

2. Aluminum vs. Copper

This chart is exclusively for copper. If you are feeding a subpanel using SER (Service Entrance Rated) aluminum cable—which is common for 100A to 200A runs due to cost—aluminum has lower ampacity. For example, a 2/0 AWG copper wire handles 175A, but a 2/0 AWG aluminum wire only handles 135A at 75°C. Always check the aluminum-specific columns in NEC 310.16 if you are not using copper.

3. Local AHJ Amendments

While the NEC allows 14 AWG for 15A lighting circuits, many local Authorities Having Jurisdiction (AHJs) ban 14 AWG entirely in new residential construction, mandating 12 AWG as the absolute minimum wire size for any branch circuit. Always check your local municipal code before buying bulk wire.

The Default Recommendation: If you want to eliminate guesswork, avoid voltage drop issues, and pass inspection in strict municipalities, standardize your entire home's general lighting and receptacle wiring on 12 AWG NM-B with 20A breakers. The marginal increase in copper cost is easily offset by the elimination of 14 AWG inventory and the ability to plug high-draw appliances into any room without tripping a 15A breaker.