Electrical Wire Sizing & Voltage Drop Calculator

Size copper and aluminum conductors (AWG / kcmil) to limit circuit voltage drop according to National Electrical Code (NEC) standards.
Electrical Analysis Summary
Calculated Voltage Drop
0.00 V
Percentage Drop (%)
0.00 %
Voltage at Load Terminal
0.0 V
Power Loss in Conductor
0.0 W
Recommended Min. Gauge for Selected Drop Limit
12 AWG
Compliance Status
OK

Electrical Engineering Formulas & NEC Guidelines

Excessive voltage drop across long conductor runs causes equipment inefficiency, motor overheating, flickering lights, and wasted energy dissipated as heat.

1. Voltage Drop Equations

For Single-Phase AC and DC circuits (2-wire systems):

ΔV = (2 * K * I * L) / CM

For Three-Phase AC circuits (balanced line-to-line):

ΔV = (1.732 * K * I * L) / CM

  • K = Conductor resistivity constant (approx. 12.9 Ω·cmil/ft for Copper; 21.2 Ω·cmil/ft for Aluminum at 75°C)
  • I = Load current in Amperes
  • L = One-way length of the run in feet
  • CM = Conductor cross-sectional area in Circular Mils

2. National Electrical Code (NEC) Standards (Article 210.19 & 215.2)

The NEC recommends that branch circuit conductors be sized so that the maximum voltage drop does not exceed 3% at the farthest outlet. The maximum combined drop for both feeder conductors and branch circuits combined should not exceed 5% for overall system operating efficiency.

3. Standard AWG Conductor Cross-Section Reference

AWG / kcmil Size Circular Mils (cmil) Typical 75°C Copper Ampacity (THHN)
14 AWG 4,110 20 A (Max 15A Breaker)
12 AWG 6,530 25 A (Max 20A Breaker)
10 AWG 10,380 35 A (Max 30A Breaker)
8 AWG 16,510 50 A
6 AWG 26,240 65 A
4 AWG 41,740 85 A
2 AWG 66,360 115 A
1/0 AWG 105,600 150 A
4/0 AWG 211,600 230 A