If you are looking for the standard wire gauge chart to size a residential branch circuit or feeder, the direct answer relies on NEC Table 310.16. For standard copper wire in a typical home installation (60°C to 75°C terminations), the baseline rules are: 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 chart without understanding the temperature columns and derating factors is how wires melt inside conduit. This guide provides the complete, bookmark-friendly data table, explains exactly which column applies to your specific installation, and maps out a concrete decision tree so you never have to guess your breaker size again.
• 15A Circuit: 14 AWG Copper (60°C Column) → 15A Breaker
• 20A Circuit: 12 AWG Copper (60°C Column) → 20A Breaker
• 30A Circuit: 10 AWG Copper (60°C Column) → 30A Breaker
• 50A Circuit: 6 AWG Copper (75°C Column) → 50A Breaker
• 100A Feeder: 2/0 AWG Aluminum (75°C Column) → 100A Breaker
How to Read the NEC 310.16 Wire Gauge Chart
The National Electrical Code (NFPA 70) publishes ampacity limits in Table 310.16. When you look at a spec sheet for THHN or NM-B (Romex) wire, you will see three distinct temperature columns: 60°C, 75°C, and 90°C. Knowing which column applies to your installation is the most common point of failure for DIYers.
Here is the golden rule of terminations, governed by NEC 110.14(C): Your wire ampacity is limited by the lowest temperature rating of any connected device, terminal, or splice.
Almost all standard residential receptacles, switches, and breakers under 100 amps are rated for 60°C or 75°C terminations. Even if you pull 90°C THHN wire through your conduit, you must size your breaker based on the 60°C or 75°C column, because the breaker terminal itself will overheat if you push 90°C-level current into it. The 90°C column is strictly used as your starting baseline before applying derating factors for heat and bundling.
Master AWG Ampacity Table (Copper & Aluminum)
The following data is sourced directly from NFPA 70 (NEC) Table 310.16 for not more than three current-carrying conductors in a raceway or cable, at an ambient temperature of 30°C (86°F).
| AWG / kcmil Size | Copper 60°C (NM-B) | Copper 75°C (THHN Term) | Copper 90°C (THHN Wire) | Aluminum 75°C (Feeder) |
|---|---|---|---|---|
| 14 AWG | 15A | 20A | 25A | -- |
| 12 AWG | 20A | 25A | 30A | -- |
| 10 AWG | 30A | 35A | 40A | -- |
| 8 AWG | 40A | 50A | 55A | 30A |
| 6 AWG | 55A | 65A | 75A | 40A |
| 4 AWG | 70A | 85A | 95A | 55A |
| 3 AWG | 85A | 100A | 115A | 65A |
| 2 AWG | 95A | 115A | 130A | 75A |
| 1 AWG | 110A | 130A | 145A | 100A |
| 1/0 AWG | 125A | 150A | 170A | 120A |
| 2/0 AWG | 145A | 175A | 195A | 135A |
| 3/0 AWG | 165A | 200A | 225A | 155A |
| 4/0 AWG | 195A | 230A | 260A | 180A |
Derating Factors: When the Base Chart Lies
The table above assumes you have three or fewer current-carrying conductors in a conduit and an ambient temperature of 86°F (30°C). If your installation deviates from this, the base ampacity drops. This is where the 90°C column saves your project.
According to OSHA and NEC safety guidelines, bundling wires traps heat. If you pull four to six current-carrying conductors through a single conduit, you must multiply the wire's base ampacity by 80%. If you have seven to nine conductors, you multiply by 70%.
Worked Example: You need to run two 20A circuits (four current-carrying hot and neutral wires) plus a ground wire through a single EMT conduit.
- Wrong Way: Looking at the 60°C column for 12 AWG (20A) and assuming it's fine. If you apply the 80% derating factor to 20A, you get 16A. A 20A breaker will trip or melt the wire.
- Right Way: Use the 90°C column for 12 AWG THHN (30A). Apply the 80% derating factor: 30A x 0.80 = 24A. Because 24A is greater than your 20A breaker, 12 AWG THHN is perfectly legal and safe. (Note: You still terminate on a 20A breaker, satisfying the 110.14(C) termination rule).
Decision Tree: Picking Your Exact Wire and Breaker
Use this decision matrix to lock in your materials list. This path assumes standard residential copper branch circuits (NM-B or THHN in conduit with standard 75°C breakers) and accounts for the NEC 125% continuous load rule (loads expected to run for 3 hours or more).
| If Your Max Load Is... | Is it Continuous? (3+ Hrs) | Required Wire Capacity | Concrete Pick: Copper Wire | Concrete Pick: Breaker |
|---|---|---|---|---|
| 12 Amps | No | 12A | 14 AWG | 15A |
| 12 Amps | Yes (x 1.25 = 15A) | 15A | 14 AWG | 15A |
| 16 Amps | No | 16A | 12 AWG | 20A |
| 16 Amps | Yes (x 1.25 = 20A) | 20A | 12 AWG | 20A |
| 24 Amps | No | 24A | 10 AWG | 25A or 30A |
| 24 Amps | Yes (x 1.25 = 30A) | 30A | 10 AWG | 30A |
| 32 Amps | No (EV Charger) | 32A | 8 AWG | 40A |
| 40 Amps | Yes (x 1.25 = 50A) | 50A | 6 AWG | 50A |
Decision Default: If your calculated load falls between standard breaker sizes (e.g., you need 31A of capacity), the NEC allows you to round up to the next standard breaker size (35A or 40A), provided your wire ampacity meets or exceeds the calculated load before rounding.
What This Chart Cannot Tell You
The NEC 310.16 wire gauge chart is strictly a thermal limit chart. It tells you the point at which the insulation will melt or degrade. It completely ignores voltage drop.
If you are running a 240V circuit to a detached garage or a well pump 150 feet away, a 10 AWG wire might be thermally rated for the 30A load, but the resistance of the copper over that distance will cause the voltage at the destination to sag below 228V (a 5% drop). Motors will overheat, and electronics will brown out.
For any run exceeding 75 feet, you must calculate voltage drop using the formula: VD = (2 x K x I x D) / CM (where K is 12.9 for copper, I is current, D is one-way distance, and CM is circular mils of the wire). If your voltage drop exceeds 3% for a branch circuit, you must upsize your wire by one or two AWG steps, regardless of what the ampacity chart dictates. Always verify long-run calculations with a dedicated voltage drop calculator or consult your local Authority Having Jurisdiction (AHJ), as local inspectors may have strict enforcement rules that supersede general NEC informational notes.
