AWG to mm² Conversion: A Complete Reference Guide
Everything you need to know about converting between AWG and metric wire sizes
When working on electrical projects that span different countries or standards, you will often need to convert between AWG (American Wire Gauge) and the metric mm² system used by IEC and most of the world. This guide provides the conversion table, the underlying formula, and practical guidance on choosing the right wire when an exact match does not exist.
How AWG is Calculated
The AWG scale is logarithmic. It is based on the number of drawing steps needed to produce a wire from a standard rod. The formula is: diameter (mm) = 0.127 × 92^((36 - AWG) / 39). From diameter, the cross-sectional area in mm² = π/4 × diameter². This means each decrease of 6 AWG approximately doubles the cross-sectional area. AWG 4/0 (largest common gauge, 107.2 mm²) through AWG 40 (smallest) covers the full range.
Common AWG to mm² Conversions
AWG 14 = 2.08 mm², AWG 12 = 3.31 mm², AWG 10 = 5.26 mm², AWG 8 = 8.37 mm², AWG 6 = 13.3 mm², AWG 4 = 21.2 mm², AWG 2 = 33.6 mm², AWG 1/0 = 53.5 mm², AWG 2/0 = 67.4 mm², AWG 3/0 = 85.0 mm², AWG 4/0 = 107.2 mm². These are exact calculated values based on the AWG formula using nominal strand dimensions.
IEC Standard Sizes and Their Nearest AWG Equivalent
IEC cross-sections are: 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120 mm². The nearest AWG matches: 1.5 mm² ≈ AWG 16, 2.5 mm² ≈ AWG 14, 4 mm² ≈ AWG 12, 6 mm² ≈ AWG 10, 10 mm² ≈ AWG 8, 16 mm² ≈ AWG 6, 25 mm² ≈ AWG 4, 35 mm² ≈ AWG 2, 50 mm² ≈ AWG 1/0, 70 mm² ≈ AWG 2/0, 95 mm² ≈ AWG 3/0, 120 mm² ≈ AWG 4/0. Note these are approximate — the actual areas are different, so ampacity values also differ.
Why You Cannot Simply Substitute Metric for AWG
While the areas are similar, the ampacity tables differ between NEC and IEC because they assume different installation methods, insulation types, and ambient temperatures. A 2.5 mm² IEC cable rated at 24 A under IEC method C is NOT equivalent to an AWG 14 rated at 15 A under NEC 60°C column, even though both are close to 2.08–2.5 mm² area. Always use the ampacity table from the applicable standard, not just convert the area.
Practical Tips for International Projects
When you need to substitute between systems, always round up to the larger size. If calculation requires 5.0 mm² and the available IEC sizes are 4 mm² and 6 mm², use 6 mm². If you must use AWG in an IEC jurisdiction, specify the equivalent area in mm² and verify ampacity from the IEC table for that installation method. Document any substitutions and verify with the local authority having jurisdiction (AHJ) before installation.
FAQ
Is AWG 12 the same as 3.31 mm²?
Geometrically yes: AWG 12 calculates to 3.31 mm² cross-sectional area. However, the nearest IEC standard size is 2.5 mm² (smaller) or 4 mm² (larger). For installations requiring IEC compliance, you would use 4 mm² to ensure adequate cross-section, even though 3.31 mm² is the exact AWG 12 area.
What is the formula to convert AWG to mm²?
Step 1: diameter (mm) = 0.127 × 92^((36 - AWG) / 39). Step 2: area (mm²) = π/4 × diameter². For AWG 12: diameter = 0.127 × 92^(24/39) = 2.053 mm; area = π/4 × 2.053² = 3.31 mm². For quick reference, use the conversion table in our AWG Converter tool.
Does the conversion change for stranded wire?
The nominal cross-sectional area is the same for solid and stranded wire of the same AWG or mm² rating. However, stranded wire has a slightly larger outside diameter than solid because of the air gaps between strands. For conduit fill calculations, use the outside diameter of the insulated cable (from NEC Chapter 9 Table 5), not the bare conductor diameter.