The standard reference for sizing copper conductors in residential branch circuits and feeders is NEC Table 310.16. For standard terminations, 14 AWG handles 15 amps, 12 AWG handles 20 amps, 10 AWG handles 30 amps, and 8 AWG handles 40 amps. Sizing wire correctly is not just about preventing a fire; it is about matching the conductor's thermal limits to the breaker's trip curve and the termination ratings of your devices. Below is the complete, decision-forward wire size and amperage chart you need to pull the right cable from the spool without a second trip to the supply house.
How to Read the Wire Size and Amperage Chart
Before looking at the numbers, you must understand the three temperature columns: 60°C (140°F), 75°C (167°F), and 90°C (194°F). These columns represent the insulation rating of the wire (like THHN or XHHW) and the temperature rating of the equipment terminations (the breaker lugs and receptacle screws).
The chart below assumes copper conductors in an ambient temperature of 86°F (30°C) or less, with no more than three current-carrying conductors in a single raceway. If you are using aluminum (like SER cable for feeders), you must use the aluminum-specific columns in the NEC, which require larger gauges for the same amperage.
Master Wire Size and Amperage Chart (Copper, THHN/THWN-2)
Source: National Electrical Code (NFPA 70), Table 310.16. Allowable ampacities of insulated copper conductors rated up to and including 2000 Volts.
| AWG / kcmil | 60°C (140°F) Column | 75°C (167°F) Column | 90°C (194°F) Column |
|---|---|---|---|
| 14 | 15A * | 20A * | 25A * |
| 12 | 20A * | 25A * | 30A * |
| 10 | 30A * | 35A * | 40A * |
| 8 | 40A | 50A | 55A |
| 6 | 55A | 65A | 75A |
| 4 | 70A | 85A | 95A |
| 3 | 85A | 100A | 110A |
| 2 | 95A | 115A | 130A |
| 1 | 110A | 130A | 145A |
| 1/0 | 125A | 150A | 170A |
| 2/0 | 145A | 175A | 195A |
| 3/0 | 165A | 200A | 225A |
| 4/0 | 195A | 230A | 260A |
* Critical NEC 240.4(D) Exception: The asterisks denote the 'Small Conductor Rule'. Even though 12 AWG wire has an ampacity of 30A in the 90°C column, NEC 240.4(D) strictly limits the overcurrent protection (breaker) for 14 AWG to 15A, 12 AWG to 20A, and 10 AWG to 30A for standard branch circuits. You cannot put a 25A breaker on 12 AWG wire, regardless of the 75°C column.
Quick-Jump Rows for the Most Queried Circuits
Bookmark this section for the most common residential DIY and rough-in scenarios. These picks assume standard copper NM-B (Romex) or THHN in conduit, with 75°C rated breakers.
- 15A Lighting & General Receptacles: 14 AWG minimum (12 AWG preferred for voltage drop mitigation on long runs). Breaker: 15A Single-Pole.
- 20A Kitchen, Bath & Garage Receptacles: 12 AWG. Breaker: 20A Single-Pole.
- 30A Dryer or Water Heater: 10 AWG. Breaker: 30A Double-Pole.
- 40A Electric Range or EV Level 2 Charger: 8 AWG. Breaker: 40A Double-Pole.
- 50A Hot Tub or Welder Outlet: 6 AWG. Breaker: 50A Double-Pole.
- 60A Subpanel Feeder: 4 AWG Copper (or 2 AWG Aluminum). Breaker: 60A Double-Pole.
- 100A Subpanel Feeder: 3 AWG Copper (or 1/0 Aluminum). Breaker: 100A Double-Pole.
Derating: How Bundle Size and Ambient Heat Modify Your Pick
The master chart above assumes ideal conditions: an ambient temperature of 86°F (30°C) and no more than three current-carrying conductors (CCCs) in a single conduit. When you deviate from this, you must apply derating factors, which modify your base ampacity value downward.
1. Conduit Fill (Bundle Derating): If you pull multiple circuits through the same EMT or PVC conduit, the wires heat each other up.
• 4 to 6 CCCs: Multiply the 90°C column ampacity by 80%.
• 7 to 9 CCCs: Multiply the 90°C column ampacity by 70%.
2. Ambient Temperature: If your conduit runs through an attic that reaches 110°F (43°C), you must multiply the 90°C column ampacity by the temperature correction factor (0.87 for 90°C wire at 110°F).
Decision Tree: Picking Your Exact Wire and Breaker Combo
Use this decision path to terminate your sizing process with one concrete pick. Never guess; follow the math.
| Step | Action & Calculation | Example: 32A Continuous EV Charger |
|---|---|---|
| 1. Calculate Continuous Load | Multiply the continuous load (runs for 3+ hours) by 1.25 (125%). | 32A × 1.25 = 40A minimum circuit ampacity. |
| 2. Size the Breaker | Select the next standard breaker size that is ≥ your Step 1 result (Standard sizes: 15, 20, 30, 40, 50, 60). | 40A is a standard size. Pick a 40A Double-Pole Breaker. |
| 3. Select Wire Gauge | Look at the Master Chart. Find the wire where the 75°C column is ≥ the breaker size. (Obey 240.4(D) limits for 14/12/10 AWG). | 8 AWG has a 75°C rating of 50A. Pick 8 AWG Copper. |
| 4. Verify Derating | Apply conduit fill or ambient heat multipliers to the 90°C column. Ensure result ≥ breaker size. | Assume 1 circuit in conduit (no derating). 8 AWG is confirmed. |
What This Chart Cannot Tell You (Voltage Drop & Local Code)
While the NEC Table 310.16 wire size and amperage chart dictates the minimum wire size to prevent the insulation from melting and the breaker from tripping, it completely ignores voltage drop.
NEC Informational Note 310.14 recommends keeping voltage drop under 3% for branch circuits and 5% overall for feeder + branch. If you are running a 20A circuit to a detached workshop 150 feet away, 12 AWG wire will safely carry the current without tripping the breaker, but the voltage at the receptacle might drop to 112V under load, causing motors to overheat and tools to stall. The fix: For any copper run exceeding 100 feet at 80% of the circuit's rated load, upsize your wire by at least one AWG (e.g., use 10 AWG instead of 12 AWG for a 20A circuit) to maintain voltage integrity.
Finally, always verify local amendments. Some municipalities require 12 AWG as the absolute minimum for all general lighting and receptacle circuits, effectively banning 14 AWG from residential construction to reduce fire risk and future-proof for higher loads. When in doubt, your local Authority Having Jurisdiction (AHJ) and the inspector's clipboard have the final say over any reference chart.
