How to Read This AWG Cross Section Table
American Wire Gauge (AWG) defines a wire's physical diameter, but the AWG cross section—measured in square millimeters (mm²) or thousands of circular mils (kcmil)—is what actually dictates current-carrying capacity, electrical resistance, and conduit fill. When sourcing wire internationally or calculating precise voltage drop, you must convert the AWG gauge to its true cross-sectional area.
The table below synthesizes physical dimensions from NEC Chapter 9, Table 8 and ampacity ratings from NEC Table 310.16 (for copper conductors, 30°C ambient). Here is how to read the columns and determine which applies to your installation:
- Cross Section (mm² / kcmil): The actual area of the conductive metal. Use mm² for IEC/international standard calculations and voltage drop formulas.
- 60°C Column: Applies to NM-B (Romex) cable, UF-B cable, and any circuit rated 100A or less where the termination temperature is unknown. This is your default column for standard residential branch circuits.
- 75°C Column: Applies to THHN/THWN wire in conduit and circuits rated over 100A, provided the lugs and breakers are explicitly rated for 75°C.
- 90°C Column: Never use this column for final breaker sizing. It is used exclusively as the starting point for derating calculations (e.g., adjusting for high ambient temperatures or multiple wires in a single conduit).
Complete AWG to mm² and kcmil Cross Section Chart
The following data applies to solid and standard stranded copper conductors. For aluminum, physical cross sections remain identical, but ampacity drops significantly (consult NEC 310.16 aluminum columns).
| AWG Size | Diameter (mm) | Cross Section (mm²) | Cross Section (kcmil) | 60°C Ampacity (A) | 75°C Ampacity (A) | 90°C Ampacity (A) |
|---|---|---|---|---|---|---|
| 14 | 1.63 | 2.08 | 4.11 | 15* | 15* | 25 |
| 12 | 2.05 | 3.31 | 6.53 | 20* | 20* | 30 |
| 10 | 2.59 | 5.26 | 10.4 | 30* | 30* | 40 |
| 8 | 3.26 | 8.37 | 16.5 | 40 | 50 | 55 |
| 6 | 4.11 | 13.30 | 26.3 | 55 | 65 | 75 |
| 4 | 5.19 | 21.15 | 41.7 | 70 | 85 | 95 |
| 3 | 5.83 | 26.67 | 52.6 | 85 | 100 | 115 |
| 2 | 6.54 | 33.62 | 66.4 | 95 | 115 | 130 |
| 1 | 7.35 | 42.41 | 83.7 | 110 | 130 | 145 |
| 1/0 | 8.25 | 53.49 | 106 | 125 | 150 | 170 |
| 2/0 | 9.27 | 67.43 | 133 | 145 | 175 | 195 |
| 3/0 | 10.40 | 85.01 | 168 | 165 | 200 | 225 |
| 4/0 | 11.68 | 107.2 | 212 | 195 | 230 | 260 |
*Note on small conductors: While 14, 12, and 10 AWG have higher physical ampacities at 90°C, NEC 240.4(D) strictly limits their overcurrent protection (breaker size) to 15A, 20A, and 30A respectively, regardless of insulation temperature rating.
Quick-Jump: The Most Queried Wire Sizes
Bookmark this section for the most common residential and light-commercial branch circuits. These values assume copper wire and standard termination limits.
14 AWG (2.08 mm²): Lighting circuits. Max breaker: 15A.
12 AWG (3.31 mm²): Standard 120V receptacles, kitchen small-appliance circuits. Max breaker: 20A.
10 AWG (5.26 mm²): Electric dryers (120V components), water heaters, 30A RV outlets. Max breaker: 30A.
8 AWG (8.37 mm²): 40A circuits, larger EV chargers, cooktops. Max breaker: 40A.
6 AWG (13.3 mm²): 50A hardwired EV chargers, subpanel feeders (small). Max breaker: 60A (at 75°C).
4 AWG (21.2 mm²): 60A-85A subpanel feeders, heavy machinery. Max breaker: 85A (at 75°C).
2 AWG (33.6 mm²): 100A service entrance (copper) or 125A subpanels. Max breaker: 115A (at 75°C).
Derating and Conduit Fill: Modifying the Base Value
The ampacities listed above assume an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a raceway. When you exceed these conditions, you must apply derating factors to the 90°C column to find your adjusted ampacity, then verify it against the termination temperature limits.
Worked Example: You are pulling four 12 AWG THHN current-carrying conductors through a single conduit for a multi-wire branch circuit.
- Start with the 90°C ampacity for 12 AWG: 30A.
- Consult NEC Table 310.15(C)(1) for 4-6 conductors: The derating factor is 80%.
- Calculate adjusted ampacity: 30A × 0.80 = 24A.
- Check termination limits: The wire terminates on a standard 75°C breaker and receptacle. The 75°C limit for 12 AWG is 20A.
- Final Result: Your wire is physically capable of 24A, but the terminations are limited to 20A. You must protect this circuit with a 20A breaker.
For a deeper dive into the physics of conductor heating and resistance, the All About Circuits wire sizing guide provides excellent foundational theory on how cross-sectional area directly impacts thermal dissipation.
Decision Path: Picking Your Wire Cross Section
Use this decision matrix to terminate your planning phase with a concrete material pick. Stop guessing and pull the correct wire from the spool.
| Application Scenario | Continuous Load | Distance | Insulation Type | Concrete Pick (AWG / mm²) |
|---|---|---|---|---|
| Standard Bedroom / Living Room Receptacles | 15A - 20A | < 100 ft | NM-B (Romex) | 12 AWG (3.31 mm²) Copper |
| Hardwired Level 2 EV Charger (48A continuous) | 48A (Requires 60A OCPD) | < 50 ft | THHN in Conduit | 6 AWG (13.3 mm²) Copper |
| 100A Detached Garage Subpanel Feeder | 100A | < 100 ft | THHN in Conduit | 3 AWG (26.7 mm²) Copper OR 1/0 AWG (53.5 mm²) Aluminum |
| 200A Main Service Entrance | 200A | < 50 ft | THHN / XHHW-2 | 2/0 AWG (67.4 mm²) Copper OR 4/0 AWG (107.2 mm²) Aluminum |
What This Table Cannot Tell You
A cross-section and ampacity chart is a baseline, not a complete engineering document. Before finalizing your materials list, account for these three variables that the table ignores:
1. Voltage Drop Over Distance
Ampacity dictates if the wire will melt; cross section and distance dictate if your equipment will actually run. A 12 AWG (3.31 mm²) wire is rated for 20A, but if you run it 200 feet to a shed, the voltage drop will exceed the recommended 3% threshold. For runs over 100 feet, you must upsize the wire cross section (e.g., moving to 10 AWG or 8 AWG) purely to maintain voltage, even if the breaker size remains 20A.
2. Stranding Class and Conduit Fill
The mm² values above represent the copper area, not the physical footprint inside your conduit. Standard Class B stranded wire has small air gaps between the strands. Highly flexible Class K wire (like welding cable) uses thousands of micro-strands, resulting in a much larger overall outside diameter for the exact same copper cross section. If you are pulling flexible wire, you must use the manufacturer's specific outside diameter for your conduit fill calculations (NEC Chapter 9, Table 1), not the bare mm² cross section.
3. Aluminum vs. Copper Oxidation
While you can achieve the same ampacity using a larger cross section of aluminum (e.g., 1/0 AWG aluminum instead of 3 AWG copper for a 100A feeder), aluminum requires specific termination practices. You must use anti-oxidant paste (like Noalox) and torque the lugs to exact manufacturer specifications to prevent thermal runaway at the breaker lugs. Never assume aluminum and copper can be treated identically just because their ampacities match on a chart.
