The physical diameter of standard solid copper wire ranges from 0.0641 inches (14 AWG) up to 0.4600 inches (4/0 AWG). However, the actual size wire gauge chart below provides more than just physical dimensions; it maps American Wire Gauge (AWG) sizes to their cross-sectional area and allowable ampacity across three distinct insulation temperature ratings (60°C, 75°C, and 90°C). All ampacity values in this reference are sourced directly from NFPA 70 (NEC) Table 310.16 for copper conductors with an ambient temperature of 30°C (86°F).
How to Read This Actual Size Wire Gauge Chart
Before pulling wire or sizing a breaker, you must understand how to read the columns in the table below. The chart is divided into physical geometry (diameter and area) and thermal limits (ampacity columns).
Which Ampacity Column Applies to Your Installation?
The most common mistake DIYers and junior apprentices make is using the 90°C column because they bought 90°C THHN wire. According to OSHA and NEC 110.14(C), you must size your overcurrent protection based on the lowest temperature rating of any connected terminal, device, or conductor in the circuit.
- 60°C Column: Applies to residential branch circuits rated 100A or less, or using 14 AWG through 1 AWG wire. Standard residential breakers and receptacles are typically rated for 60°C or 75°C, but the NEC mandates the 60°C column for these smaller sizes as a conservative safety baseline.
- 75°C Column: Applies to circuits rated over 100A, or wire sizes 1/0 AWG and larger. Most modern commercial lugs and main panel bus bars are rated 75°C.
- 90°C Column: This column is never used to directly size a breaker for standard terminations. It is used exclusively as the mathematical starting point for derating calculations (explained below) and for high-temp equipment terminations specifically rated for 90°C.
The Complete AWG Wire Size and Ampacity Reference Table
| AWG Size | Diameter (inches) | Diameter (mm) | Area (kcmil) | 60°C Ampacity (A) | 75°C Ampacity (A) | 90°C Ampacity (A) |
|---|---|---|---|---|---|---|
| 14 AWG * | 0.0641 | 1.628 | 4.11 | 15 | 20 | 25 |
| 12 AWG * | 0.0808 | 2.053 | 6.53 | 20 | 25 | 30 |
| 10 AWG * | 0.1019 | 2.588 | 10.4 | 30 | 35 | 40 |
| 8 AWG * | 0.1285 | 3.264 | 16.5 | 40 | 50 | 55 |
| 6 AWG | 0.1620 | 4.115 | 26.2 | 55 | 65 | 75 |
| 4 AWG | 0.2043 | 5.189 | 41.7 | 70 | 85 | 95 |
| 3 AWG | 0.2294 | 5.827 | 52.6 | 85 | 100 | 110 |
| 2 AWG * | 0.2576 | 6.543 | 66.4 | 95 | 115 | 130 |
| 1 AWG | 0.2893 | 7.348 | 83.7 | 110 | 130 | 150 |
| 1/0 AWG | 0.3249 | 8.252 | 106 | 125 | 150 | 170 |
| 2/0 AWG * | 0.3648 | 9.266 | 133 | 145 | 175 | 195 |
| 3/0 AWG | 0.4096 | 10.40 | 168 | 165 | 200 | 225 |
| 4/0 AWG | 0.4600 | 11.68 | 212 | 195 | 230 | 260 |
* Note: Per NEC 240.4(D), overcurrent protection for 14 AWG is strictly capped at 15A, 12 AWG at 20A, 10 AWG at 30A, and 8 AWG copper at 40A for standard residential branch circuits, regardless of higher ampacities listed in the 75°C or 90°C columns.
What This Chart Cannot Tell You (Derating & Edge Cases)
An actual size wire gauge chart provides base ampacities under ideal conditions: a single conductor in free air, or no more than three current-carrying conductors in a raceway, at an ambient temperature of 30°C (86°F). Real-world jobsites rarely match these ideal parameters.
How Derating Rows Modify the Base Value
When you pull more than three current-carrying conductors through a single conduit (like a multi-wire branch circuit or a 3-phase feeder), the wires heat each other up. You must apply an adjustment factor from NEC Table 310.15(C)(1).
Worked Example: You are pulling four 10 AWG THHN current-carrying conductors through a single EMT conduit to feed a 240V/120V multi-wire branch circuit.
- Find the base 90°C ampacity: The chart above shows 10 AWG at 90°C is 40A.
- Apply the derating factor: For 4-6 conductors, the NEC mandates an 80% multiplier. (40A × 0.80 = 32A).
- Check terminal limits: Your derated wire can now only safely carry 32A. However, because your breaker and receptacle terminals are rated 60°C/75°C, NEC 110.14(C) caps your final allowable ampacity at the 60°C column value for 10 AWG, which is 30A.
- Result: You must protect this circuit with a 30A breaker. If you needed a 40A circuit, 10 AWG would fail the derating math, and you would need to upsize to 8 AWG.
Other Missing Variables
- Voltage Drop: This chart assumes short runs. If your run exceeds 100 feet, the resistance of the copper will cause voltage drop. You must calculate voltage drop using the exact resistance values found in NEC Chapter 9, Table 8, aiming for a maximum 3% drop on branch circuits.
- Ambient Temperature: If your conduit runs across a hot attic or a rooftop where ambient temperatures exceed 86°F (30°C), you must apply temperature correction factors from NEC Table 310.15(B)(1), which will reduce the allowable ampacity.
Wire Gauge Sizing FAQ
How do I measure the actual size of an unmarked wire gauge?
Never measure the outside diameter of insulated wire to determine AWG; the insulation thickness varies wildly between THHN, NM-B, and UF-B. Strip back an inch of insulation and measure the bare copper conductor using a digital caliper or a dedicated wire gauge measuring tool. Match the bare copper diameter (in inches or mm) to the second or third column of the chart above. If the wire is stranded, you must measure the cross-sectional area or use a gauge tool with a notch-and-slot design, as stranded wire has a slightly larger overall diameter than solid wire of the same AWG due to the air gaps between strands.
Why is my 90°C THHN wire limited to 60°C ampacity on the actual size wire gauge chart?
This is dictated by the "weakest link" rule in NEC 110.14(C). While the PVC/nylon insulation on THHN wire can safely withstand 90°C without melting, the brass and copper terminals inside standard residential breakers, receptacles, and switches are only tested and rated to dissipate heat up to 60°C or 75°C. If you push 90°C worth of current into a 60°C terminal, the terminal will overheat, oxidize, and eventually cause a fire, even if the wire insulation itself remains intact. Therefore, the 60°C column governs the final breaker size for smaller residential circuits.
Does the actual size wire gauge chart apply to aluminum wire?
No. The table above is exclusively for copper conductors. Aluminum has a higher electrical resistance and a lower melting point at the terminations, meaning it requires a larger physical diameter to carry the same current safely. For example, while 4 AWG copper is rated for 85A at 75°C, you must use 2 AWG aluminum to achieve that same 90A/75°C rating. Always consult the aluminum-specific columns in NEC Table 310.16 when sizing SER cable or aluminum feeder wires for subpanels.
How does voltage drop change the wire size I need from this chart?
The ampacity chart only tells you the maximum current the wire can handle before the insulation degrades or the breaker trips; it does not guarantee that 120V will actually arrive at the end of a long run. For example, pulling 15A through 100 feet of 14 AWG wire will result in a voltage drop of roughly 6 volts (5%), which can cause motors to overheat and lights to dim. To maintain a 3% maximum drop on a 120V circuit over 100 feet, you would need to upsize from 14 AWG to 12 AWG or even 10 AWG, entirely independent of the base ampacity chart.
