Wire Gauge Calculator

Professional tools for electrical wire sizing

Wire Size Calculator

Enter your circuit parameters to calculate the minimum wire gauge required:

Copper
Aluminum
Minimum Wire Size (AWG)
--
Minimum Wire Size (mm²)
--
Actual Voltage Drop
-- %
Power Loss
-- W

Important Notes:

  • AWG = American Wire Gauge (smaller number = thicker wire)
  • For high-power applications, use thicker wire than calculated
  • Copper wire resistivity: 1.68×10⁻⁸ Ω·m (at 20°C)
  • For long distances, voltage drop becomes critical
  • Consider current carrying capacity (ampacity) for continuous loads

AWG Reference Table

American Wire Gauge (AWG) to metric conversion and current capacity:

AWG Diameter (mm) Cross-section (mm²) Max Current (A)* Resistance (Ω/km)

Notes:

  • *Maximum current ratings are approximate for copper wire at 60°C
  • Actual current capacity depends on insulation type, ambient temperature, and installation conditions
  • For continuous loads, use 80% of maximum current rating
  • Resistance values are for copper wire at 20°C

Wire Sizing Theory

Ohm's Law and Wire Resistance

Wire resistance is calculated using the formula:

R = ρ × L / A

Where:

  • R = Resistance (Ω)
  • ρ = Resistivity (Ω·m) - 1.68×10⁻⁸ for copper
  • L = Length (m) - multiply by 2 for round trip
  • A = Cross-sectional area (m²)

Voltage Drop Calculation

Voltage drop across a wire is calculated using:

Vdrop = I × R

Where:

  • Vdrop = Voltage drop (V)
  • I = Current (A)
  • R = Wire resistance (Ω)

The percentage voltage drop is: (Vdrop / Vsystem) × 100%

Power Loss

Power lost as heat in the wire is:

Ploss = I² × R

This represents energy wasted as heat and affects system efficiency.

Wire Sizing Guidelines

  • 3% voltage drop - Maximum for most applications
  • 5% voltage drop - Acceptable for lighting circuits
  • Motor circuits - Consider starting current (6-8× normal)
  • Long runs - Use thicker wire to minimize losses
  • High current - Check wire ampacity ratings