Voltage Drop Calculator

Calculate voltage drop for copper or aluminum wire by AWG gauge, distance, and current.

Conductor Material

Wire Gauge (AWG)

One-Way Distance

feet

Load Current

amps

System Voltage

Voltage Drop

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Drop %

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Voltage at Load

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NEC Voltage Drop Guidelines

The National Electrical Code (NEC) recommends keeping voltage drop to 3% or less for branch circuits and 5% or less total (feeder + branch combined). While these are recommendations rather than hard requirements in most cases, exceeding them can cause equipment to underperform, overheat motors, and shorten appliance lifespans.

The formula used is: V_drop = 2 × R × I × (distance / 1000), where R is the resistance per 1,000 feet from standard wire tables. The factor of 2 accounts for the round-trip current path (hot and neutral/return conductors).

Aluminum conductors have approximately 61% of the conductivity of copper, giving them about 1.61× the resistance per foot at equivalent gauge. Aluminum is commonly used for service entrances and large feeders where cost savings are significant.