Voltage Drop Calculator

What is voltage drop?

Voltage drop is the loss of electrical potential caused by wire resistance and, in AC circuits, reactance. Excessive drop can lead to dim lights, weak heater performance, and motors running hotter than expected.

A common practical target is to keep voltage drop below 5% at full load. Better conductor material, larger wire size, shorter runs, and lower current all help reduce drop.

Major causes of voltage drop

• Wire material: Copper generally has lower resistance than aluminum.
• Wire size: Larger conductors reduce resistance and drop.
• Distance: Longer one-way runs increase total drop.
• Load current: More current increases voltage loss.

Voltage drop formulas

Ohm’s Law base relation: Vdrop = I × R.

Single-phase AC or DC approximation: Vdrop = 2 × I × R × L.

Three-phase approximation: Vdrop = √3 × I × R × L.

In this tool, values use resistance in Ω/1000 ft and one-way distance in feet. AC modes include power factor and reactance effects.