When converting between North American and international wire sizing standards, the most common mistake is confusing diameter with cross-sectional area. American Wire Gauge (AWG) is a logarithmic stepped system based on the physical diameter of the conductor, while the metric system uses square millimeters (mm²) to denote the actual cross-sectional area. For the most queried residential sizes: 14 AWG equals 2.08 mm², 12 AWG equals 3.31 mm², and 10 AWG equals 5.26 mm². Because metric wire is manufactured in discrete steps (1.5, 2.5, 4, 6 mm²), you cannot buy an exact 1:1 metric equivalent for most AWG sizes; you must round up to the next standard IEC metric size to maintain safe ampacity.

Below is the definitive reference for translating between these systems, combining physical dimensions with the legal ampacity limits enforced on jobsites.

The Master Wire AWG to mm² Conversion Table (NEC & IEC)

How to read this table: The 'Area' column shows the exact mathematical cross-section of the bare copper. The 'Closest IEC Metric' column shows the standard international wire size you would substitute if working on a metric-spec project. The 'NEC Ampacity' column reflects the allowable current for copper conductors with 75°C insulation (like THHN/THWN-2) in a standard 30°C ambient environment, sourced directly from NFPA 70 (National Electrical Code) Table 310.16. Physical dimensions are calculated per The Engineering Toolbox AWG reference and IEC 60228 standards.

Bookmark Quick-Jumps: Click the highlighted rows below for the most common residential branch circuit sizes.
AWG Size Diameter (mm) Exact Area (mm²) Closest IEC Metric (mm²) NEC Ampacity (75°C Cu)
14 AWG 1.628 2.08 2.5 mm² 20A (15A Breaker Limit)
12 AWG 2.053 3.31 4.0 mm² 25A (20A Breaker Limit)
10 AWG 2.588 5.26 6.0 mm² 35A (30A Breaker Limit)
8 AWG 3.264 8.37 10.0 mm² 50A (40A Breaker Limit)
6 AWG 4.115 13.30 16.0 mm² 65A
4 AWG 5.189 21.15 25.0 mm² 85A
3 AWG 5.827 26.67 35.0 mm² 100A
2 AWG 6.544 33.62 35.0 mm² 115A
1 AWG 7.348 42.41 50.0 mm² 130A
1/0 AWG 8.251 53.49 50.0 mm² 150A
2/0 AWG 9.266 67.43 70.0 mm² 175A
3/0 AWG 10.405 85.01 95.0 mm² 200A
4/0 AWG 11.684 107.20 120.0 mm² 230A

Which Column Applies and How Derating Modifies Base Values

The ampacity column above assumes a best-case scenario: no more than three current-carrying conductors in a raceway, and an ambient temperature not exceeding 30°C (86°F). In the real world, your installation conditions will force you to modify these base values using the derating tables found in NEC 310.15(C)(1) and 310.15(B)(1).

Understanding the Temperature Columns:
Wire insulation like THHN is rated for 90°C, but you rarely get to use that full capacity. NEC 110.14(C) dictates that the ampacity of a circuit is limited by the lowest temperature rating of any connected component. Since most residential breakers, receptacles, and terminal lugs are rated for 75°C, the final allowable ampacity after all derating is applied cannot exceed the 75°C column. However, you must start your derating calculations using the 90°C column if you are using THHN wire in conduit.

A Real-World Derating Example:
Imagine you are pulling four current-carrying conductors (two 240V circuits sharing a neutral, or a multi-wire branch circuit setup) through a single EMT conduit. According to NEC Table 310.15(C)(1), four to six conductors require an 80% adjustment factor.

  • Step 1: You want to protect the circuit at 30A, so you look at 10 AWG wire.
  • Step 2: The 90°C ampacity for 10 AWG THHN is 40A.
  • Step 3: Apply the 80% derating factor: 40A × 0.80 = 32A.
  • Step 4: Check the termination limit. The derated value (32A) is well below the 75°C column limit for 10 AWG (35A), so the wire is protected.

If you had tried to use 12 AWG wire for this same conduit run, the 90°C base is 30A. Derated at 80%, that drops to 24A. Because 24A is below your required 30A load, you would be forced to upsize to 10 AWG, even though a standard single-circuit 12 AWG run would normally handle a 20A load.

NM-B (Romex) Exception: If you are running standard yellow NM-B cable inside a wall, the insulation is only rated for 60°C. You cannot use the 90°C column for derating NM-B. You must derate from the 60°C baseline, which severely limits its use in high-ambient areas like attics in the southern US.

What This Table Cannot Tell You (And When to Call an Electrician)

While a wire AWG to mm conversion chart gives you the physical and thermal baselines, it completely ignores three critical engineering factors that dictate whether a wire will actually perform safely in your specific application.

1. Voltage Drop Over Distance
Ampacity only tells you if the wire will melt or degrade the insulation. It does not tell you if the voltage at the end of the run will be sufficient to operate the load. NEC 310.15(B) Informational Note recommends keeping voltage drop under 3% for branch circuits and 5% overall. If you are running a 12 AWG (3.31 mm²) wire 150 feet to a 120V, 15A receptacle, the wire won't overheat, but the voltage drop will exceed 6%, causing motors to run hot and lights to dim. For long runs, you must use a voltage drop calculator and typically upsize the wire by one or two AWG steps, regardless of the breaker size.

2. Stranded vs. Solid Outer Diameter
The diameters listed in the table above represent the bare copper conductor. If you are using stranded wire (like THHN), the overall diameter of the copper bundle is physically larger than a solid core wire of the same AWG due to the air gaps between the strands. Furthermore, once you add the insulation, the outer diameter (O.D.) increases significantly. If you are calculating conduit fill capacity per NEC Chapter 9, Table 1, you must use the manufacturer's specific insulated O.D., not the bare copper diameter from this chart. Forcing too many 10 AWG stranded wires into a 1/2-inch EMT conduit will result in jamming and damaged insulation during the pull.

3. Metric Lug and Terminal Compatibility
If you are integrating imported European machinery (wired in IEC metric sizes) into a North American panel (wired in AWG), physical compatibility at the terminal block becomes a major issue. A 6.0 mm² metric wire has an area of 6.0 mm², which falls between 10 AWG (5.26 mm²) and 8 AWG (8.37 mm²). If you strip a 10 AWG wire and insert it into a terminal block designed and torqued specifically for 6.0 mm² metric wire, the set screw may not achieve the correct clamping force, leading to a high-resistance connection, arcing, and eventual thermal failure. Always use ferrules or verify the terminal manufacturer's specific AWG/mm² cross-compatibility matrix before terminating mixed-standard wires.

Finally, remember that local Authorities Having Jurisdiction (AHJ) and municipal inspectors always have the final say on wire sizing and installation methods. This chart serves as NEC-style guidance for planning and material estimation, but any permanent installation involving mains voltage, subpanels, or service feeders should be verified against your local electrical code amendments or performed by a licensed electrician.