The correct wire size for any circuit depends on the conductor material, insulation temperature rating, and installation method. The wire gauge and ampacity chart below provides the maximum allowable continuous current for copper conductors based on NEC Table 310.16. For standard residential branch circuits using NM-B (Romex), you will primarily use the 60°C column. For individual THHN/THWN conductors in conduit terminating at 75°C rated lugs, use the 75°C column. The 90°C column is strictly reserved as a baseline for derating calculations.
How to Read This Wire Gauge and Ampacity Chart
Before pulling wire, you must identify which temperature column applies to your specific installation. The ampacity of a circuit is limited by the weakest link in the chain—usually the termination points (breakers, lugs, and receptacles), not the wire insulation itself.
- 60°C Column: Applies to all NM-B (Romex) cable assemblies per NEC 334.80, regardless of the 90°C stamp on the internal wire insulation. It also applies to any equipment or terminals explicitly marked for 60°C, and all 14, 12, and 10 AWG circuits by default.
- 75°C Column: Applies to individual THHN/THWN wires in conduit when terminating on modern breakers and lugs rated for 75°C (standard for most panels and subpanels manufactured after 1995).
- 90°C Column: Never use this column for final breaker sizing. It is only used as the mathematical starting point when applying ambient temperature or bundling derating factors.
Additionally, NEC 240.4(D) imposes strict overcurrent protection limits on small conductors. Even if the 90°C column lists 12 AWG at 30A, the maximum breaker size for 14 AWG is 15A, for 12 AWG is 20A, and for 10 AWG is 30A, unless specific motor or HVAC exceptions apply.
Complete Copper Wire Gauge and Ampacity Chart
Use the quick-jump links below to find the most commonly queried residential and light-commercial circuit sizes. All values assume copper conductors, an ambient temperature of 30°C (86°F), and no more than three current-carrying conductors in a raceway.
- 15A Circuits (14 AWG)
- 20A Circuits (12 AWG)
- 30A Circuits (10 AWG)
- 50A Circuits (6 AWG / 8 AWG)
- 100A Subpanels (3 AWG / 4 AWG)
- 200A Services (4/0 AWG)
| AWG Size | Area (kcmil) | 60°C (NM-B / 60°C Terminals) | 75°C (THHN / 75°C Terminals) | 90°C (Derating Baseline Only) |
|---|---|---|---|---|
| 14 | 4,110 | 15A* | 20A | 25A |
| 12 | 6,530 | 20A* | 25A | 30A |
| 10 | 10,380 | 30A* | 35A | 40A |
| 8 | 16,510 | 40A | 50A | 55A |
| 6 | 26,240 | 55A | 65A | 75A |
| 4 | 41,740 | 70A | 85A | 95A |
| 3 | 52,620 | 85A | 100A | 110A |
| 2 | 66,360 | 95A | 115A | 130A |
| 1 | 83,690 | 110A | 130A | 145A |
| 1/0 | 105,600 | 125A | 150A | 170A |
| 2/0 | 133,100 | 145A | 175A | 195A |
| 3/0 | 167,800 | 165A | 200A | 225A |
| 4/0 | 211,600 | 195A | 230A | 260A |
*Asterisk denotes sizes restricted by NEC 240.4(D) overcurrent protection limits for small conductors.
How Derating Modifies Your Base Ampacity
The values 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. When you deviate from these conditions, you must apply correction and adjustment factors to the 90°C column (for THHN/THWN) to find your true adjusted ampacity.
Example: Bundling Derating
Imagine you are pulling six current-carrying 12 AWG THHN conductors through a single EMT conduit for a multi-wire branch circuit setup. According to NEC Table 310.15(C)(1), 4 to 6 current-carrying conductors require an 80% adjustment factor.
1. Start at the 90°C column for 12 AWG: 30A.
2. Apply the 80% bundling factor: 30A × 0.80 = 24A.
3. Check the final ampacity: The wire can safely carry 24A. However, NEC 240.4(D) still mandates that 12 AWG copper cannot be protected by a breaker larger than 20A. Therefore, you must still use a 20A breaker, but the wire will run significantly cooler in the conduit than if you had only pulled three wires.
Example: Ambient Temperature Correction
If that same conduit runs through an attic where the ambient temperature reaches 110°F (43°C), you must apply a temperature correction factor. For 90°C insulation at 41-45°C, the factor is 0.87.
Adjusted Ampacity = 30A (base) × 0.80 (bundling) × 0.87 (temperature) = 20.88A. In this scenario, the derated wire ampacity drops below the 240.4(D) breaker limit, meaning you must upsize to 10 AWG THHN to maintain a safe 20A circuit.
This wire gauge and ampacity chart strictly defines thermal limits (how much current the wire can handle before the insulation melts). It does not account for voltage drop. Over long distances, wire resistance causes voltage to sag, which can damage motors and cause LED flicker. For runs exceeding 50 feet on a 120V circuit, or 100 feet on a 240V circuit, consult Chapter 9, Table 8 resistance values and upsize your wire by at least one AWG to maintain a maximum 3% branch circuit voltage drop.
Frequently Asked Questions
What size wire do I need for a 50 amp breaker?
For a standard 50A circuit (like an EV charger or electric range), you need 6 AWG copper THHN/THWN if your breaker and receptacle terminals are rated for 75°C, which is standard for modern equipment. If you are using NM-B (Romex) cable, or if the equipment is only rated for 60°C, you must use 4 AWG copper. Never use 8 AWG for a 50A breaker, even though some outdated internet forums suggest it; 8 AWG is strictly limited to 40A at 60°C and 50A at 75°C, leaving zero thermal headroom for continuous loads, which require conductors sized at 125% of the load (62.5A for a 50A continuous EV charger).
Can I use the 90°C column for NM-B Romex wire?
No. Even though the individual conductors inside a modern NM-B jacket are insulated with 90°C rated material (typically THHN), NEC Article 334.80 explicitly states that the ampacity of NM-B cable must be determined using the 60°C column of Table 310.16. You may use the 90°C rating of the internal wires solely for calculating derating factors (like ambient temperature adjustments in a hot attic), but the final derated ampacity cannot exceed the 60°C column value. For 12 AWG NM-B, the absolute maximum ampacity is 20A, period.
Does this wire gauge and ampacity chart apply to aluminum conductors?
No, the chart above is exclusively for copper. Aluminum has a higher electrical resistance and different thermal expansion properties, requiring larger gauges for the same current. For example, while a 100A subpanel feeder requires 3 AWG copper, it requires 1/0 AWG aluminum (using the 75°C column). If you are sizing aluminum wire for a 200A residential service, you must use 4/0 AWG aluminum (specifically AA-8000 series alloy as required by NEC 310.14), not copper. Always ensure your panel lugs are rated for aluminum (marked AL or CU/AL) and apply an anti-oxidant compound like Noalox to the terminations.
How does voltage drop change my wire gauge choice?
Ampacity charts ensure the wire won't catch fire; voltage drop calculations ensure your equipment actually works. NEC 210.19(A) Informational Note recommends a maximum 3% voltage drop for branch circuits and 5% for the total feeder plus branch. If you are wiring a 20A, 120V receptacle at the end of a 150-foot run using 12 AWG copper, the voltage drop will be roughly 9.6V (8%), which is unacceptable. To fix this, you must ignore the ampacity chart's minimums and upsize to 8 AWG copper, which drops the loss to roughly 3.8V (3.1%), bringing it within acceptable engineering limits.
