CONDUCTORS · CALCULATOR

Voltage drop calculator

Free voltage drop calculator: get voltage drop from voltage, current, one-way cable length, conductor area and resistivity at operating temperature.

Written by Chameera Sampath · Not yet reviewed by a licensed electrician. See the methodology.

US (NEC) only · NFPA 70 / NEC — locally adopted editionDefaults are US values. Verify the locally adopted NEC edition and project data.Official reference ↗

Project inputs

Measurements

Voltage

Current

One-way cable length

Conductor area

kcmil

Resistivity at operating temperature

Ω·cmil/ft

Supply

Set area from AWG (geometric equivalent)

Resistivity starting point:Override with project temperature / manufacturer data.

Updates as inputs change. Unit changes preserve the same physical values.

THE MATH BEHIND THE ANSWER

Method & assumptions

ΔV = k × I × ρ × L / A; k = 2 or √3

Resistance-only estimate; reactance and AC power factor are excluded. Does not establish ampacity.

Results do not check every aspect of an electrical installation. The calculators follow US (NEC) practice only; a regional preset changes defaults such as voltage and units, and no result certifies NEC compliance.

Sources and validation →

Worked example

Voltage: 120 V · Current: 20 A · One-way cable length: 100 ft · Conductor area: 6.53 kcmil · Resistivity at operating temperature: 12.9 Ω·cmil/ft · Supply: Single phase

Voltage drop: 7.902 V · Drop percentage: 6.585 %

This example uses the stated inputs; results for the entered values appear above.

Explore the conductors branch →See the related electrical concepts →Size the wire by ampacity and voltage drop →See the standard breaker sizes →Read the AWG wire gauge chart →All wire sizing pages, 20 A to 200 A →

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