AWG Wire Ampacity Estimate

I_max ≈ 10^((40 − AWG)/15)

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Result
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Formula

I_max ≈ 10^((40 − AWG) / 15)

Description

This empirical formula provides a rough estimate of the maximum current capacity (ampacity) of copper wire in free air. The actual ampacity depends heavily on insulation temperature rating, ambient temperature, bundling, and whether the wire is in free air or enclosed in conduit. NEC (National Electrical Code) tables provide the authoritative values for building wiring. This estimate is useful for quick sanity checks and initial wire sizing in electronics applications where NEC does not directly apply (PCB wiring, internal equipment wiring).

Variables

  • AWG — American Wire Gauge number (0-40)

Practical Notes

Approximate values: AWG 30 ≈ 0.86 A, AWG 24 ≈ 3.5 A, AWG 20 ≈ 11 A, AWG 16 ≈ 22 A, AWG 12 ≈ 41 A, AWG 10 ≈ 55 A. These are rough estimates for chassis wiring in free air with standard PVC insulation. For power wiring per NEC, values are typically 50-70% of these free-air values. For high-flex applications (robot cables, test leads), upsize by 2-4 AWG for reduced heating and longer flex life.

Related Formulas

Wire Resistance AWG to Cross-Section Area Cable Voltage Drop Maximum Cable Length Skin Effect AC Resistance Coaxial Cable Impedance

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