If you are wiring a standard 20-amp residential branch circuit, you need 12 AWG copper wire. If you are running a 50-amp feed for an EV charger or electric range, you need 6 AWG copper or 4 AWG aluminum. But for every other load, you need a reliable, code-compliant reference.
This wire size chart by amps provides the exact ampacity ratings for copper and aluminum conductors based on the National Electrical Code (NEC). Before pulling wire, you must understand how to read the temperature columns, apply derating factors, and recognize the physical limits this chart does not cover.
The Master Wire Size Chart by Amps (NEC Table 310.16)
The following data is extracted directly from NEC Table 310.16 (formerly 310.15(B)(16)). It assumes an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway or cable.
| AWG / kcmil Size | 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 AWG | 15A | — | — | — | — |
| 12 AWG | 20A | 25A | 30A | — | — |
| 10 AWG | 30A | 35A | 40A | — | — |
| 8 AWG | 40A | 50A | 55A | 30A | 40A |
| 6 AWG | 55A | 65A | 75A | 40A | 50A |
| 4 AWG | 70A | 85A | 95A | 55A | 65A |
| 3 AWG | 85A | 100A | 115A | 65A | 75A |
| 2 AWG | 95A | 115A | 130A | 75A | 90A |
| 1 AWG | 110A | 130A | 145A | 85A | 100A |
| 1/0 AWG | 125A | 150A | 170A | 100A | 120A |
| 2/0 AWG | 145A | 175A | 195A | 115A | 135A |
| 3/0 AWG | 165A | 200A | 225A | 130A | 155A |
| 4/0 AWG | 195A | 230A | 260A | 150A | 180A |
- 15 Amps: 14 AWG Copper (60°C column)
- 20 Amps: 12 AWG Copper (60°C column)
- 30 Amps: 10 AWG Copper (60°C column)
- 40 Amps: 8 AWG Copper (75°C column)
- 50 Amps: 6 AWG Copper (75°C column)
- 100 Amps: 3 AWG Copper or 1 AWG Aluminum (75°C column)
How to read this table: The ampacity values represent the maximum continuous current the wire can carry without exceeding the temperature rating of its insulation. Notice that smaller wires (14, 12, 10 AWG) do not have aluminum ratings listed; the NEC generally prohibits aluminum conductors smaller than 8 AWG for standard branch circuit wiring due to termination and oxidation risks.
Which Temperature Column Applies to Your Installation?
The most common mistake DIYers and junior electricians make is looking at the 90°C column because modern THHN/THWN-2 wire is rated for 90°C, and assuming they can use that higher ampacity. You almost always cannot.
Under NEC 110.14(C), the allowable ampacity of a circuit is dictated by the lowest temperature rating of any connected component, termination, or conductor in the entire run. This is known as the 'weakest link' rule.
- The 60°C Column: Use this for circuits rated 100 amps or less, or for conductors sized 14 AWG through 1 AWG, unless the equipment is specifically marked otherwise. Most standard residential breakers and receptacles fall into this category, which is why 14 AWG is capped at 15A and 12 AWG at 20A, despite their insulation being capable of more.
- The 75°C Column: Use this for circuits rated over 100 amps, or for conductors larger than 1 AWG. Most modern commercial panels, lugs, and heavy-duty breakers are rated for 75°C terminations.
- The 90°C Column: You can only use this column for the final ampacity if every single termination point (breaker, lug, disconnect) is explicitly rated for 90°C, which is exceptionally rare in standard building wiring. However, the 90°C column is legally used as the starting point for calculating derating factors (explained below).
Derating Factors: When the Base Chart Isn't Enough
The wire size chart by amps assumes two ideal conditions: an ambient temperature of exactly 30°C (86°F), and no more than three current-carrying conductors bundled together in a conduit. When real-world conditions violate these assumptions, you must apply derating factors from NEC Table 310.15(C)(1) and Table 310.15(B)(1).
Here is how derating modifies the base value in a practical scenario:
Imagine you are pulling four current-carrying conductors (two 240V circuits sharing a neutral, or just four hot wires) through a single PVC conduit to a subpanel. You want to use 10 AWG THHN copper wire protected by a 30-amp breaker.
- Find Base Ampacity: Look at the 90°C column for 10 AWG THHN. The base ampacity is 40A.
- Apply Bundling Derating: NEC Table 310.15(C)(1) states that 4 to 6 current-carrying conductors require an 80% adjustment factor.
- Calculate Derated Ampacity: 40A × 0.80 = 32A.
- Check Termination Limits: The breaker lugs are rated 75°C. The 75°C column for 10 AWG is 35A.
- Final Verdict: You must use the lower of the derated 90°C value (32A) and the 75°C termination value (35A). The final allowable ampacity is 32A. Since 32A is greater than your 30A load and breaker, 10 AWG is perfectly legal and safe.
If you had attempted this same run with four 12 AWG wires, the derated 90°C ampacity would be 24A (30A × 0.80). However, NEC 240.4(D) strictly limits 12 AWG copper to a 20-amp overcurrent device regardless of derating math, forcing you to upsize to 10 AWG for a 30A circuit in a bundled scenario.
What This Wire Size Chart Cannot Tell You
While this chart is the definitive guide for thermal ampacity, it does not account for the physics of long wire runs or physical space constraints. Relying solely on ampacity can lead to failed inspections or poorly performing equipment.
1. Voltage Drop Over Distance
Ampacity tells you if the wire will melt; it does not tell you if the voltage at the end of the run will be sufficient to operate the load. The NEC recommends a maximum 3% voltage drop on branch circuits and 5% overall from the service entrance to the furthest outlet.
For example, a 50-amp EV charger located 150 feet from the panel requires 6 AWG copper based purely on the ampacity chart. However, pushing 40 continuous amps through 150 feet of 6 AWG copper results in a voltage drop of roughly 4.8% on a 240V circuit. To maintain optimal charging performance and keep the drop under 3%, you must upsize to 4 AWG copper, even though the ampacity chart says 6 AWG is thermally safe.
2. Conduit Fill Capacity
NEC Chapter 9, Table 1 limits conduit fill to 40% when pulling three or more wires. You might calculate that four 4/0 AWG conductors are perfect for a 200-amp residential feeder based on the ampacity chart, but you cannot physically fit four 4/0 THHN wires into a standard 1.5-inch PVC conduit. You would need to upsize to 2-inch conduit or switch to parallel runs, which introduces a whole new set of NEC 310.10(G) requirements.
3. Short-Circuit Withstand Ratings
The chart assumes normal operating currents. Under a dead-short fault condition, thousands of amps can flow for milliseconds before the breaker trips. Smaller wires can vaporize or fuse to terminal blocks before the magnetic trip in the breaker clears the fault. Always ensure your overcurrent protective device's let-through current rating matches the withstand rating of the conductors and busbars in your panel.
