What is the maximum recommended voltage drop for electrical circuits?

Standard electrical codes typically recommend a maximum voltage drop of 3% for branch circuits and 5% overall from the service entrance to the farthest outlet.

How does the calculator handle three-phase circuits compared to single-phase?

For single-phase and DC circuits, the calculator multiplies the resistance by 2 to account for the return path. For balanced three-phase circuits, it applies a factor of √3 (1.732).

Can I input wire sizes in both AWG and metric units?

Yes, you can toggle the Size Input Mode between AWG wire gauge sizes and metric cross-sectional area in square millimeters (mm²).

Does conductor material affect the voltage drop calculation?

Yes, copper has lower resistivity (1.68e-8 Ω·m) than aluminum (2.82e-8 Ω·m), meaning aluminum conductors will experience a higher voltage drop for the same size and length.

What temperature is assumed for the conductor resistivity?

The calculator uses standard resistivity values measured at 20 °C (68 °F) for both copper and aluminum.

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Cable Voltage Drop Calculator

Compute cable voltage drop from current, length, conductor size (AWG/mm²) and material, for DC, single-phase and three-phase circuits

Details

What this tool helps you do

Voltage drop is the loss of voltage along a conductor due to its resistance.

Equations:

One-way resistance: R = ρ · L / A
Copper ρ = 1.68e-8 Ω·m, Aluminum ρ = 2.82e-8 Ω·m at 20 °C
DC / single-phase: Vdrop = 2 · I · R
Balanced three-phase: Vdrop = √3 · I · R
Percent drop: ΔV / Vsource · 100
Line loss: Ploss = I² · Rtotal

Typical limits: ≤3% for sensitive circuits, ≤5% total. AWG uses the standard copper Ω/km table, scaled for aluminum.

Execution

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Prepared example runs

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2 examples

15 A over 30 m of 12 AWG copper at 120 V

Typical branch circuit — drop and load-end voltage.

Three-phase 400 V, 25 A, 50 m of 6 mm² copper

Industrial feeder example using metric cable sizing.

<div>Three-phase drop with √3 factor applied.</div>

Inputs

Set the required fields, then run the tool.

8 options

SettingsAdjust formats, ranges, numbers, and modes.8

Current (I)numberRequiredOne-way Cable Length (m)numberRequiredConductor MaterialselectOptionalSize Input ModeselectOptionalAWG SizeselectOptionalCross-sectional Area (mm²)numberOptionalCircuit TypeselectOptionalSource Voltage (V)numberRequired

Result

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Samples

Cable Voltage Drop Calculator

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Key facts

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Use cases

Examples

1. Sizing a 120V Residential Branch Circuit

2. Industrial Three-Phase Feeder Calculation

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