🔌 Voltage Drop Calculator
Estimate the voltage drop across a wire run based on its length, cross-sectional area, current, and conductor material.
What is voltage drop?
Voltage drop is the reduction in voltage that occurs as electrical current travels through the resistance of a wire. Longer runs, smaller conductors, and higher currents all increase voltage drop, which can cause dim lighting, inefficient motors, or equipment that underperforms if the drop is too large. Many electrical codes recommend keeping voltage drop under about 3-5% for typical branch circuits.
How this calculator works
The calculator uses the standard resistive voltage drop formula Vd = (k × L × I × ρ) / A, where L is the one-way cable length, I is the load current, ρ is the conductor material’s resistivity, and A is the cross-sectional area. The factor k accounts for the circuit type: 2 for a single-phase circuit (current travels out and back), or √3 for a balanced three-phase circuit.
This tool gives a general engineering estimate for planning purposes. Real installations should be verified against the applicable local electrical code and, for critical circuits, checked by a qualified electrician or engineer.