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AWG Wire Gauge & Voltage Drop

Calculate physical properties of AWG solid copper wire and predict voltage drop and loop resistance.

Input Parameters
Wire Physical specs
Wire Diameter—
Cross Sectional Area—
Total Round-Trip Resistance—
Line Losses & Drop
Voltage Drop—
Voltage Drop Rate—
Safety & Drop Rating:
—
Based on voltage-drop %: <3% PASS · 3–5% WARNING · >5% FAIL. If FAIL, use a thicker wire (lower AWG number), a shorter run, or a higher supply voltage.
💡 Usage & Formula

AWG Diameter Formula (ASTM B258): d = 0.127 × 92^((36-AWG)/39) mm. The cross-sectional area is A = (π/4) × d².

Copper Temperature Correction: Copper resistivity increases with temperature. The formula applied is ρ_T = ρ_20 × (1 + α(T - 20)) where ρ_20 = 1.7241 × 10^-8 Ω·m and α = 0.00393 / °C.

Voltage Drop: V_drop = I × R_total where R_total is calculated for the round-trip wire length (2 × One-Way Length).

Safety & Drop Rating grades the drop %: <3% PASS, 3–5% WARNING, >5% FAIL. A FAIL means the drop is too large (load under-voltage & wire heating) — pick a thicker wire (lower AWG number), shorten the run, or raise the supply voltage.

When you need it: Choosing a wire gauge for a current and run length, then checking the resulting voltage drop and self-heating before you commit to a harness.

Worked example: 18 AWG is about 0.82 mm² and ~2.3 mΩ/ft. Carrying 5 A over a 10 ft round trip (20 ft of copper) drops 5 × 0.046 Ω ≈ 0.23 V.

Tips & gotchas:

  • Three AWG numbers lower doubles the copper area and roughly halves the resistance.
  • Size for both ampacity (heating) and voltage drop — on long runs the drop is usually the tighter limit.
  • Bundling wires and higher ambient temperature both derate the safe current.
  • Count the full loop length (out and back) when computing drop, not just the one-way distance.
📖 References: American wire gauge (Wikipedia) · AWG Wire Gauge Chart (Engineering Toolbox)