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AWG to mm² Converter

Convert between American Wire Gauge (AWG) and metric mm² cable sizes

Reference Info & Formulas
Safe UK Round-Up
AWGExactUK Safe142.082.5 mm²123.314.0 mm²105.266.0 mm²88.3710 mm²613.316 mm²421.225 mm²233.635 mm²1/053.570 mm²

Always round UP to the next UK standard size for BS 7671 compliance.

Rules of Thumb

Rule of 3: ↓3 AWG sizes ≈ doubles the area

Rule of 6: ↓6 AWG sizes ≈ doubles the diameter

Rule of 10: ↓10 sizes ≈ 10× the area

JIS Sizes (HVAC)

Japanese equipment (Daikin, Mitsubishi) uses non-standard sizes:

JIS 2.0→ use 2.5 mm²JIS 3.5→ use 4.0 mm²JIS 5.5→ use 6.0 mm²
Input
Select direction and cable size

Data: ASTM B258 (AWG standard), IEC 60228 (metric sizes)

For guidance only. The responsibility for any electrical installation lies with the qualified person carrying out the work. Always verify calculations independently and apply professional judgement.

How This Calculator Works

AWG (American Wire Gauge) and metric mm² are two different systems for specifying conductor size. This calculator converts between them using the standard AWG formula.

AWG uses an inverse logarithmic scale — smaller gauge numbers indicate larger conductors. The system originated in the wire-drawing industry, where each gauge number represented one additional pass through a drawing die. Metric sizing measures the copper cross-sectional area directly in square millimetres, which is the standard used in BS 7671 and throughout the UK.

d = 0.127 × 92^((36 − n) / 39) mm
d
= Conductor diameter in mm
n
= AWG gauge number

ASTM B 258

The cross-sectional area is then calculated from the diameter: A = π × (d/2)². Since AWG sizes rarely align with standard metric sizes, the calculator also shows the nearest standard BS 7671 cable size for practical use.

Quick Reference — AWG to mm² Conversions

Common AWG sizes with metric equivalents

ASTM B 258 / BS 7671 Table 4D5
AWGExact mm²Nearest BS 7671 SizeTypical Use (US)
180.821.0mm²Low-voltage control, thermostat
161.311.5mm²Light-duty extension cords
142.082.5mm²Lighting circuits (15A)
123.314.0mm²Socket circuits (20A)
105.266.0mm²Cookers, dryers (30A)
88.3710.0mm²Sub-panels, large appliances
613.3016.0mm²Service entrance, sub-feeds

Always round up to the next standard metric size. Using a smaller metric cable than the AWG equivalent is non-compliant.

Practical Notes

Always Round Up

When converting AWG to metric, always select the next standard metric size that meets or exceeds the AWG cross-sectional area. A 12 AWG cable at 3.31mm² is not equivalent to 2.5mm² — you must use 4mm² minimum for BS 7671 compliance.

Terminal Compatibility

Terminal mismatch is a fire risk. An undersized conductor in an oversized terminal will not grip properly, creating a high-resistance joint that generates heat. Always verify the terminal clamping range against the actual conductor cross-section, not just the nominal size.

Tri-rated Cable

Tri-rated cable carries AWG, metric mm², and CSA markings on the same sheath. For UK installations, always use the mm² value for BS 7671 compliance, cable selection, and recording on certificates.

Frequently Asked Questions

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