The physical bare diameter of standard solid copper wire ranges from 0.0641 inches (14 AWG) to 0.1019 inches (10 AWG) for the most common residential branch circuits. However, picking a wire size requires looking past the bare metal diameter to the insulation type, temperature rating, and NEC ampacity tables. This reference chart provides the exact AWG diameters, cross-sectional areas, and maximum ampacities for copper conductors, giving you the exact numbers needed to size your next home wiring run without a second trip to the electrical supply house.
How to Read the AWG Diameters and Ampacity Table
Before pulling wire, you need to understand which columns in the chart below apply to your specific installation. The table is divided into physical dimensions (governed by ASTM B258 standards) and electrical limits (governed by NEC Article 310.16).
Complete AWG Diameters and Sizing Reference Chart
Below is the comprehensive lookup table for solid and stranded copper wire. Bookmark this section for quick reference when calculating voltage drop or conduit fill.
| AWG Size | Bare Diameter (in) | Bare Diameter (mm) | Area (kcmil) | 75°C Ampacity (Copper) | Max Standard Breaker |
|---|---|---|---|---|---|
| 14 AWG | 0.0641 | 1.628 | 4.11 | 20A (15A max breaker) | 15A |
| 12 AWG | 0.0808 | 2.053 | 6.53 | 25A (20A max breaker) | 20A |
| 10 AWG | 0.1019 | 2.588 | 10.38 | 35A (30A max breaker) | 30A |
| 8 AWG | 0.1285 | 3.264 | 16.51 | 50A | 40A / 50A |
| 6 AWG | 0.1620 | 4.115 | 26.24 | 65A | 60A |
| 4 AWG | 0.2043 | 5.189 | 41.74 | 85A | 70A / 80A |
| 3 AWG | 0.2294 | 5.827 | 52.62 | 100A | 100A |
| 2 AWG | 0.2576 | 6.543 | 66.36 | 115A | 100A / 110A |
| 1 AWG | 0.2893 | 7.348 | 83.69 | 130A | 125A |
| 1/0 AWG | 0.3249 | 8.252 | 105.6 | 150A | 150A |
| 2/0 AWG | 0.3648 | 9.266 | 133.1 | 175A | 175A |
| 3/0 AWG | 0.4096 | 10.40 | 167.8 | 200A | 200A |
| 4/0 AWG | 0.4600 | 11.68 | 211.6 | 230A | 225A / 250A |
Source: Physical dimensions per ASTM B258; Ampacities per NEC Table 310.16. Max breaker sizes reflect NEC 240.4(D) small conductor rules and standard overcurrent device availability.
Derating and Conduit Fill: Modifying the Base Value
The ampacities listed above assume no more than three current-carrying conductors in a raceway and an ambient temperature of 86°F (30°C). Real-world installations often require you to modify these base values.
How Derating Modifies the Base Value
When you pull four or more current-carrying conductors through a single conduit, the heat generated by the wires cannot dissipate efficiently. You must apply a derating factor to the 90°C column ampacity (which is higher than the 75°C column used for termination limits).
1. Base 90°C ampacity for 12 AWG is 30A.
2. Four conductors require an 80% derating factor (NEC Table 310.15(C)(1)).
3. 30A × 0.80 = 24A derated ampacity.
4. Because 24A is still greater than the 20A termination limit, you can safely use this wire on a 20A breaker. If the derated value drops below your breaker size, you must upsize the wire.
Bare Diameter vs. Insulated Diameter
The table above lists bare AWG diameters. If you are calculating conduit fill (NEC Chapter 9, Table 1), you must use the insulated diameter. For example, a 12 AWG THHN wire has a bare diameter of 0.0808 inches, but an approximate insulated outside diameter of 0.115 inches. Always consult the specific manufacturer's cut sheet (like Southwire or Cerrowire) for exact insulated dimensions before calculating conduit fill percentages, as insulation thickness varies slightly by brand.
Decision Path: Picking the Right AWG for Your Circuit
Use this decision-tree to terminate your sizing process with a concrete wire pick. These recommendations assume standard copper NM-B (Romex) or THHN in residential dry locations at standard distances (under 100 feet).
| If Your Application Is... | And the Breaker Size Is... | Then Pick This Copper AWG |
|---|---|---|
| Standard lighting, bedroom/bathroom receptacles | 15A | 14 AWG (Use 12 AWG if run exceeds 75 ft to mitigate voltage drop) |
| Kitchen small appliance, bathroom GFCI, garage, outdoor receptacles | 20A | 12 AWG (NEC requires 20A for these specific locations) |
| Electric water heater, window AC unit, RV receptacle | 30A | 10 AWG |
| Electric range/oven, large window AC, EV charger (Level 2 low power) | 40A | 8 AWG |
| Electric vehicle charger (standard Level 2), hot tub/spa | 50A | 6 AWG |
| 100A subpanel feeder (short run under 50 ft) | 100A | 3 AWG (Use 4 AWG if 90°C rated terminations are verified, otherwise 3 AWG for 75°C) |
What This Table Cannot Tell You
While this chart covers physical dimensions and baseline thermal limits, it does not account for three critical installation variables. For deeper theory on wire resistance and sizing, resources like All About Circuits provide excellent foundational physics.
- Voltage Drop Over Distance: The NEC recommends keeping voltage drop under 3% for branch circuits and 5% total for feeder + branch. If you are running a 12 AWG circuit to a detached garage 150 feet away, the physical diameter of 12 AWG is too small to prevent excessive voltage drop under a 16A continuous load. You must upsize to 10 AWG or 8 AWG based on voltage drop calculators, even though 12 AWG is thermally rated for the 20A breaker.
- Aluminum Wire Sizing: This table is strictly for copper. If you are running aluminum feeder wire (like XHHW-2 or SER cable) to a subpanel, aluminum has higher resistance and lower ampacity. The general rule is to upsize aluminum by two AWG steps compared to copper (e.g., use 2 AWG aluminum where you would use 4 AWG copper for an 80A feeder).
- Local AHJ Amendments: Some local jurisdictions amend the NEC to require 12 AWG minimum for all 15A and 20A residential receptacle circuits, effectively banning 14 AWG from new construction. Always verify with your local Authority Having Jurisdiction (AHJ) or building inspector before roughing in wire.
