Voltage drop calculator

Vdrop = 2 × L × I × ρ ÷ A. The "×2" accounts for the round-trip (out + return) of a typical DC circuit. Copper resistivity ρ ≈ 0.0172 Ω·mm²/m.

Voltage drop
0 V
—
Drop %
0%
Cross-section used
0 mm²
Voltage at load
0 V
Round-trip length
0 m

Recommended limits

  • Residential branch circuit: ≤ 3% drop (NEC informational guidance).
  • Combined feeder + branch: ≤ 5%.
  • 12 V automotive / RV: aim for ≤ 3% — voltage drop matters more at low voltage.
  • Solar PV strings: ≤ 2% on the DC side to preserve panel output.