The bare copper diameter of a 1 AWG wire is exactly 0.2893 inches (7.35 mm). When insulated with standard THHN/THWN-2, the outer diameter increases to approximately 0.330 inches (8.38 mm). For XHHW-2 insulation, the outer diameter is slightly smaller at 0.305 inches (7.75 mm). These physical dimensions are critical for calculating conduit fill, determining bending radius, and verifying that the wire will physically seat into breaker lugs and terminal blocks without damaging the insulation.
1 AWG Wire Dimensions and Ampacity Reference Table
How to read this table: The bare diameter column represents the pure copper conductor, used for calculating DC resistance and voltage drop. The insulated diameter columns (THHN and XHHW-2) represent the outer jacket, which you must use for conduit fill calculations per NEC Chapter 9. The ampacity columns are sourced directly from NEC Table 310.16 for copper conductors. Always cross-reference the insulation type printed on the wire jacket with the temperature column you intend to use.
| AWG Size | Bare Dia. (in) | THHN Dia. (in) | XHHW-2 Dia. (in) | Area (kcmil) | 75°C Amps | 90°C Amps |
|---|---|---|---|---|---|---|
| 3 AWG | 0.2294 | 0.265 | 0.245 | 52.62 | 100A | 115A |
| 2 AWG | 0.2576 | 0.295 | 0.270 | 66.36 | 115A | 130A |
| 1 AWG | 0.2893 | 0.330 | 0.305 | 83.69 | 130A | 145A |
| 1/0 AWG | 0.3249 | 0.365 | 0.340 | 105.6 | 150A | 170A |
| 2/0 AWG | 0.3648 | 0.410 | 0.380 | 133.1 | 175A | 195A |
Bench Tip: If you are pulling 1 AWG aluminum wire (such as XHHW-2 for a subpanel feeder), the physical outer diameter is identical to 1 AWG copper. However, aluminum has a lower ampacity. 1 AWG aluminum is only rated for 100A at 75°C, compared to 130A for copper.
Applying Derating and Installation Constraints
Knowing the 1 AWG cable diameter and base ampacity is only the first step. Real-world installations require adjusting these baseline numbers based on your specific environment and termination hardware.
Which Column Applies to Your Installation?
For 95% of residential and commercial branch circuits and feeders, the 75°C column (130A) is the legally binding limit. This is because standard breakers, panelboard lugs, and disconnect switches are tested and rated for 75°C terminations. Even though THHN wire is rated for 90°C (145A), you can only use the 90°C column as a starting point for derating calculations. The final adjusted ampacity cannot exceed the 75°C rating of the termination equipment.
How Derating Rows Modify the Base Value
When you bundle multiple wires together in a single raceway, they trap heat. NEC 310.15(C)(1) mandates adjustment factors for more than three current-carrying conductors. If you pull four to six current-carrying conductors through a conduit, you must apply an 80% adjustment factor.
The Math: You apply this factor to the 90°C column, not the 75°C column.
145A (90°C rating) × 0.80 = 116A.
Because 116A is lower than the 130A terminal limit, your final allowable ampacity for that 1 AWG wire drops to 116A. If your calculated load is 120A, this wire is now undersized, and you must step up to 1/0 AWG.
What the Table Cannot Tell You
This reference chart assumes an ambient temperature of 30°C (86°F) and standard installation conditions. It does not account for:
- Voltage Drop: 1 AWG copper has a resistance of approximately 0.154 ohms per 1,000 feet at 75°C. On a 120A load running 150 feet at 240V, you will experience a voltage drop of roughly 2.7%. If your run exceeds 150 feet, you must upsize to 1/0 or 2/0 AWG to maintain the recommended 3% maximum drop.
- High Ambient Temperatures: If the wire runs through an attic or boiler room where temperatures exceed 86°F (30°C), you must apply ambient temperature correction factors from NEC Table 310.15(B)(1).
- Continuous Loads: If the load runs for 3 hours or more (like an EV charger or commercial lighting), NEC 210.20 requires you to multiply the load by 125% before sizing the wire and breaker.
Conduit Fill and Bending Radius for 1 AWG
The physical diameter of the insulated cable dictates how many wires you can legally pull through a given conduit size. NEC Chapter 9 Table 1 limits conduit fill to 40% when pulling three or more wires.
Using the 0.330-inch outer diameter for 1 AWG THHN, the cross-sectional area of a single wire is 0.0855 square inches.
- 3/4-inch EMT: The 40% fill limit is 0.213 sq in. You can fit a maximum of two 1 AWG THHN wires (0.171 sq in total). You cannot fit a third wire (which would require 0.256 sq in).
- 1-inch EMT: The 40% fill limit is 0.346 sq in. You can safely pull four 1 AWG THHN wires (0.342 sq in total).
- 1-1/4-inch PVC (Schedule 40): The 40% fill limit is 0.498 sq in. You can pull up to five 1 AWG THHN wires.
When bending the conduit, remember that 1 AWG is exceptionally stiff. Use a mechanical conduit bender (hickey or ratchet bender) rather than a hand bender to prevent kinking the EMT, which would reduce the internal diameter and cause the wire to jam during the pull. Always use wire pulling lubricant rated for THHN/XHHW-2 when pulling 1 AWG or larger to reduce friction and prevent jacket tearing.
Frequently Asked Questions
What is the exact metric diameter of a 1 AWG copper wire?
The bare copper conductor diameter is exactly 7.348 mm. When coated with standard THHN/THWN-2 insulation, the overall outer diameter measures approximately 8.38 mm. If you are using metric conduit (such as PVC conduit sized in millimeters outside North America), you must use the 8.38 mm figure for your fill calculations, not the bare copper measurement.
Can I use 1 AWG aluminum wire instead of copper for a 100-amp subpanel?
Yes, 1 AWG aluminum (typically XHHW-2 or THWN-2) is perfectly legal and physically fits the same conduit as 1 AWG copper. However, 1 AWG aluminum is only rated for 100 amps at 75°C. If your subpanel main breaker is rated for 100A, 1 AWG aluminum is the exact minimum size required. If you need to feed a 120A or 125A subpanel, you must step up to 1/0 AWG aluminum.
Will 1 AWG wire fit into a standard 100-amp breaker lug?
In almost all cases, yes. Standard 100A molded case circuit breakers (MCCBs) and residential load center breakers are designed to accept wire ranges from #14 or #12 AWG up to #1 or 1/0 AWG. However, always check the specific manufacturer's lug kit data sheet. If you are terminating on older equipment or specific IEC-rated contactors, the lug might max out at #2 AWG, requiring you to use a reducing lug or a short pigtail.
How does stranding affect the outer diameter of 1 AWG cable?
Stranded 1 AWG wire has a slightly larger outer diameter than solid 1 AWG wire. While the total copper cross-sectional area remains exactly 83,690 circular mils, the microscopic air gaps between the individual copper strands force the overall bundle to be wider. For conduit fill purposes, always use the stranded diameter listed in NEC Chapter 9 Table 5, as the code accounts for this physical reality. Furthermore, stranded wire is significantly more flexible, making it much easier to pull through conduit bends than solid 1 AWG, which is rarely manufactured for building wire today.
