If you are wiring a standard residential 120V/240V circuit under 100 amps, the direct answer is to use the 60°C column for NM-B (Romex) cable and the 75°C column for THHN wire in conduit. For the most common branch circuits: 14 AWG handles 15 amps, 12 AWG handles 20 amps, 10 AWG handles 30 amps, 8 AWG handles 40 amps, and 6 AWG handles 55 amps (routinely used for 50-amp circuits). For a 100-amp subpanel feeder, use 3 AWG copper or 1/0 AWG aluminum.
But grabbing a number from a random internet table is how you end up with a melted neutral lug or a tripped breaker that won't reset. To size wire correctly, you need to understand the physics of heat dissipation and the legal framework of the National Electrical Code (NEC). Below is the definitive wire to amp chart and the decision framework to apply it to your specific installation.
How to Read the Wire to Amp Chart (The Rules of the Columns)
Before you look at the numbers, you must understand the matrix. The master wire to amp chart is derived from NFPA 70 (NEC) Table 310.16. It is divided by conductor material (Copper vs. Aluminum) and temperature rating (60°C, 75°C, and 90°C). Here is how to select your column:
The Golden Rule of Terminations (NEC 110.14(C)): Your wire ampacity is limited by the lowest temperature rating of any connected component. Most modern residential breakers and receptacles are rated for 75°C. However, NM-B (Romex) cable is physically limited to 60°C. Therefore, even if you strip NM-B and land it on a 75°C breaker, you must use the 60°C column to size the overcurrent protection.
- 60°C Column: Use this for all NM-B, NM-C, and UF-B cables. Also use this for any circuit rated 100 amps or less where the termination temperature is unknown.
- 75°C Column: Use this for THHN/THWN wires pulled in conduit, as well as SER/SEU feeder cables, provided the lugs and breakers are explicitly marked 75°C (standard for modern panels).
- 90°C Column: Never use this column to size your breaker. The 90°C rating exists solely as a mathematical starting point for derating calculations (explained below).
The Master Wire to Amp Chart (NEC Table 310.16)
The following table covers the complete range of standard residential and light-commercial wire sizes. Ampacities assume an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway.
| AWG / kcmil | Copper 60°C (NM-B) | Copper 75°C (THHN) | Aluminum 60°C | Aluminum 75°C (SER/XHHW) |
|---|---|---|---|---|
| 14 | 15A* | 20A* | - | - |
| 12 | 20A* | 25A* | - | - |
| 10 | 30A | 35A | - | - |
| 8 | 40A | 50A | 30A | 40A |
| 6 | 55A | 65A | 40A | 50A |
| 4 | 70A | 85A | 55A | 65A |
| 3 | 85A | 100A | 65A | 75A |
| 2 | 95A | 115A | 75A | 90A |
| 1 | 110A | 130A | 85A | 100A |
| 1/0 | 125A | 150A | 100A | 120A |
| 2/0 | 145A | 175A | 115A | 135A |
| 3/0 | 165A | 200A | 130A | 155A |
| 4/0 | 195A | 230A | 150A | 180A |
*Note: Per NEC 240.4(D), small conductor overcurrent protection is strictly capped. 14 AWG is capped at 15A and 12 AWG is capped at 20A, regardless of the 75°C column showing higher theoretical limits.
Quick-Jump: Most Queried Residential Circuit Sizes
Bookmark this section. These are the exact material picks for 95% of home wiring projects. Always verify local codes, as OSHA and local AHJ regulations may impose stricter rules in specific municipalities.
- 15-Amp Lighting/Receptacle Circuit: 14 AWG Copper NM-B. Breaker: 15A single-pole.
- 20-Amp Kitchen/Bath/Garage Circuit: 12 AWG Copper NM-B. Breaker: 20A single-pole (GFCI/AFCI as required).
- 30-Amp Dryer or RV Receptacle: 10 AWG Copper NM-B or THHN. Breaker: 30A double-pole.
- 40-Amp Electric Range (Older/Smaller): 8 AWG Copper NM-B or THHN. Breaker: 40A double-pole.
- 50-Amp EV Charger, Hot Tub, or Modern Range: 6 AWG Copper THHN in conduit (or 6 AWG NM-B if you accept the 55A limit and use a 50A breaker). Breaker: 50A double-pole.
- 100-Amp Subpanel Feeder: 3 AWG Copper THHN or 1/0 AWG Aluminum SER. Breaker: 100A double-pole.
- 200-Amp Main Service Entrance: 4/0 AWG Aluminum (XHHW-2 in conduit or SER cable). Breaker: 200A main.
Derating: When the Base Chart Lies to You
The wire to amp chart assumes ideal conditions: 86°F (30°C) ambient air and a maximum of three current-carrying conductors in a conduit. If you violate either assumption, the wire cannot shed heat as efficiently, and you must apply derating factors.
What the Table Cannot Tell You: NEC Table 310.16 does not account for voltage drop. If you are running a 50-amp EV charger 150 feet from the panel, 6 AWG copper will safely carry the current without melting, but the voltage at the car will drop below 220V, causing charging faults. For runs over 100 feet, always upsize your wire by one or two AWG steps to maintain a maximum 3% voltage drop.
How Derating Modifies the Base Value: When you have 4 to 6 current-carrying conductors in a single conduit, you must multiply the ampacity by 80%. For 7 to 9 conductors, multiply by 70%. Crucially, you apply this percentage to the 90°C column, not the 75°C column.
Worked Example: You are pulling two 20-amp circuits (4 current-carrying wires total: 2 hots, 2 neutrals) through a single 3/4-inch EMT conduit using 12 AWG THHN. 1. Look at the 90°C column for 12 AWG Cu (not shown in the abbreviated table above, but it is 30A in the full NEC book). 2. Apply the 80% derating factor for 4 conductors: 30A × 0.80 = 24A. 3. Because 24A is greater than your 20A breaker requirement, 12 AWG THHN is perfectly legal and safe. If you had pulled 4 circuits (8 wires), you'd derate to 70% (30A × 0.70 = 21A), which still passes, but you are getting dangerously close to the limit.
Decision Tree: Pick Your Exact Wire Size Right Now
Stop guessing. Follow this decision path to lock in your exact materials list for your next pull.
| Scenario | Conditions | Concrete Pick (Wire & Breaker) |
|---|---|---|
| Standard Indoor Wall Outlet | Living room or bedroom, standard 120V, run inside drywall cavities. | Buy: 14 AWG Copper NM-B (Romex). Breaker: 15A AFCI. |
| Kitchen Small Appliance | Countertop receptacles, high-draw appliances expected, inside drywall. | Buy: 12 AWG Copper NM-B. Breaker: 20A GFCI/AFCI. |
| Hardwired 48A EV Charger | Garage wall, surface mounted, requires 60A circuit (125% continuous load rule). | Buy: 6 AWG Copper THHN (Black, Red, Green) in 1/2" EMT conduit. Breaker: 60A double-pole. |
| 100A Detached Garage Subpanel | Underground trench, 50-foot run, 4-wire feed required. | Buy: 1/0-1/0-1/0-2 AWG Aluminum Mobile Home Feeder (URD) direct burial. Breaker: 100A double-pole in main panel. |
| 200A Main Service Upgrade | Meter to main panel, exterior wall mount, short run. | Buy: 4/0-4/0-4/0-2/0 Aluminum SER Cable. Breaker: 200A Main disconnect. |
By anchoring your material choices to the NEC temperature columns and applying derating math only when conduit fill demands it, you eliminate the risk of thermal failure at the lugs. Always torque your breaker and busbar lugs to the manufacturer's specified inch-pound rating using a calibrated torque screwdriver—this is the most common point of failure in otherwise perfectly sized circuits.
