If you are sizing a branch circuit or feeder, the direct answer for standard residential copper wire is: 14 AWG is rated for 15 amps, 12 AWG for 20 amps, 10 AWG for 30 amps, 8 AWG for 40 amps, and 6 AWG for 55 amps. However, pulling a single number from a generic internet graphic is how DIYers melt terminal lugs and fail inspections. The true authority is NEC Table 310.16, and using it correctly requires understanding temperature columns, termination ratings, and derating factors.
This reference guide provides the complete, un-truncated NFPA 70 National Electrical Code data for copper and aluminum, explains the physics behind the columns, and details the edge cases that generic charts hide.
How to Read This Wire Gauge to Amp Chart
Before jumping to the numbers, you must understand how to read the table columns. The chart is divided by conductor material (Copper vs. Aluminum) and insulation temperature rating (60°C, 75°C, and 90°C).
Furthermore, NEC 240.4(D) places hard limits on small conductors regardless of their insulation rating. Even though 14 AWG THHN has a 90°C rating of 25A, the code strictly limits its overcurrent protection to 15A. The chart below reflects these legal limits in the first three rows.
Complete NEC 310.16 Wire Gauge to Amp Chart
Quick-Jump to Most Queried Sizes: 14 AWG | 12 AWG | 10 AWG | 8 AWG | 6 AWG | 4 AWG | 2 AWG
| AWG / kcmil | Copper 60°C (140°F) | Copper 75°C (167°F) | Copper 90°C (194°F) | Aluminum 75°C (167°F) | Aluminum 90°C (194°F) |
|---|---|---|---|---|---|
| 14 | 15A * | 20A * | 25A * | — | — |
| 12 | 20A * | 25A * | 30A * | — | — |
| 10 | 30A * | 35A * | 40A * | — | — |
| 8 | 40A | 50A | 55A | — | — |
| 6 | 55A | 65A | 75A | 50A | 55A |
| 4 | 70A | 85A | 95A | 55A | 65A |
| 3 | 85A | 100A | 110A | 65A | 75A |
| 2 | 95A | 115A | 130A | 75A | 90A |
| 1 | 110A | 130A | 145A | 85A | 100A |
| 1/0 | 125A | 150A | 170A | 100A | 120A |
| 2/0 | 145A | 175A | 195A | 115A | 135A |
| 3/0 | 165A | 200A | 225A | 130A | 155A |
| 4/0 | 195A | 230A | 260A | 150A | 180A |
* Asterisks denote sizes restricted by NEC 240.4(D) for small conductors. The values shown are the maximum allowable overcurrent device ratings, not the raw insulation ampacity.
What This Chart Cannot Tell You: Derating and Voltage Drop
The table above assumes ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together. In the real world, you must apply derating factors that modify these base values.
How Derating Modifies the Base Value
Derating happens in two stages: ambient temperature correction and bundling adjustment. You apply these multipliers to the 90°C column (for THHN/THWN-2), not the 75°C column.
Worked Example: You are pulling 10 AWG THHN copper through a conduit in a Texas attic that reaches 50°C (122°F). The conduit contains 6 current-carrying conductors.
- Base Ampacity: 10 AWG in the 90°C column is 40A.
- Temperature Correction: At 50°C ambient, the correction factor for 90°C insulation is 0.82. (40A × 0.82 = 32.8A).
- Bundling Adjustment: 6 conductors in a raceway requires an 80% adjustment factor. (32.8A × 0.80 = 26.24A).
- Final Result: Your derated ampacity is 26.24A. You must protect this wire with a 25A breaker, dropping down from the standard 30A you would normally use for 10 AWG.
What the Table Cannot Tell You
- Voltage Drop: NEC 310.16 only addresses thermal limits (preventing the wire from melting). It does not account for voltage drop over distance. If you run 12 AWG copper 150 feet to a 16A window AC unit, the wire won't overheat, but the voltage at the receptacle will drop below 110V, potentially damaging the compressor motor. Always calculate voltage drop for runs over 50 feet.
- Physical Lug Sizing: A 2/0 AWG wire is rated for 175A (Copper, 75°C), but the physical lugs on a standard 100A residential main breaker might only accept up to 1/0 AWG. Always check the manufacturer's lug data sheet before buying heavy-gauge feeder wire.
- Short-Circuit Withstand: The chart assumes standard overcurrent protection. It does not tell you if the wire can survive the magnetic and thermal forces of a high-available-fault-current short circuit before the breaker trips.
Frequently Asked Questions
What size wire do I need for a 50 amp breaker?
For a standard 50A circuit (like an EV charger or subpanel feeder) using copper wire in a normal 30°C ambient environment, you need 6 AWG copper if your terminations are rated 75°C (which yields 65A), or 4 AWG copper if the terminations are only rated 60°C (which yields 70A). If you are using aluminum wire (like 4-4-4-2 mobile home feeder), you must use 4 AWG aluminum (rated 55A at 75°C). Never use 8 AWG copper for a 50A breaker; its maximum rating is 50A only if terminations are 75°C, leaving zero safety margin and violating standard sizing practices for continuous loads.
Can I use 10 gauge wire on a 40 amp breaker?
No. Under NEC 240.4(D), 10 AWG copper wire is strictly limited to a maximum 30A overcurrent protective device, regardless of whether you are using 75°C or 90°C insulation. Even though the 90°C column in the chart lists 10 AWG at 40A, that number is only a starting point for derating math. Putting a 40A breaker on 10 AWG wire is a direct code violation and a severe fire hazard. For a 40A breaker, you must step up to a minimum of 8 AWG copper.
Does the ground wire need to be the same gauge as the hot wires?
Not necessarily. The equipment grounding conductor (EGC) is sized based on the rating of the breaker, not the gauge of the current-carrying conductors, per NEC Table 250.122. For example, on a 20A breaker, a 12 AWG copper ground is required. If you upsized your hot wires to 10 AWG to mitigate voltage drop over a long distance, you are not legally required to upsize the ground wire to 10 AWG as well; 12 AWG remains sufficient. However, if you upsized the hot wires because you had to derate for heat or bundling, NEC 250.122(B) requires you to increase the ground wire proportionally.
How does wire length affect the wire gauge to amp chart?
Wire length does not change the thermal ampacity values in the wire gauge to amp chart. A 12 AWG wire can safely carry 20 amps whether it is 2 feet long or 200 feet long without melting. However, length drastically affects voltage drop. As a rule of thumb, if your one-way wire length exceeds 50 feet on a 120V circuit (or 100 feet on a 240V circuit), you should calculate the voltage drop. If the drop exceeds 3% (3.6V on a 120V circuit), you must increase the wire gauge by one size to maintain equipment efficiency, even if the chart says the smaller wire is thermally safe.
