Electrical Planning Tool

Voltage Drop Calculator

Calculate voltage loss, voltage at the load, power loss, percentage drop, and the recommended conductor size for DC, single-phase AC, and three-phase AC circuits.

Copper and aluminum
AWG and mm² sizes
Feet and meters

Plan safer electrical runs

Compare the estimated voltage drop with your selected maximum limit before choosing a cable.

Conductor performance Optimized

Enter circuit details

Use the one-way distance between the source and load.

Circuit type

Conductor material

Source voltage

Load current

One-way cable length

Maximum allowed drop

Conductor size Select AWG or enter a custom mm² value

mm²

Calculation results

Your estimated conductor performance appears below.

Estimated voltage drop

1.87 V

Within selected limit

Percentage drop 0.81%

Voltage at load 228.13 V

Power loss 37.35 W

Circuit resistance 0.0934 Ω

Cable-size estimate

The selected conductor is within the chosen voltage-drop limit.

This tool provides planning estimates. Cable ampacity, insulation, temperature, installation method, local electrical codes, fault current, and protective devices must also be checked by a qualified professional.

What is a Voltage Drop Calculator?

A Voltage Drop Calculator estimates how much electrical voltage is lost as current travels through a conductor. Every cable has electrical resistance, so the voltage available at the load can be lower than the voltage supplied at the source.

Excessive voltage drop can cause poor equipment performance, dim lighting, unreliable motors, inefficient power delivery, and additional heat in a circuit. Choosing a larger conductor or reducing the cable length can help lower this loss.

How the voltage-drop calculation works

This calculator uses conductor resistivity, conductor area, one-way cable length, current, and circuit configuration to estimate resistance and voltage loss.

DC and single-phase formula

Voltage Drop = 2 × Length × Current × Resistivity ÷ Area

Three-phase formula

Voltage Drop = √3 × Length × Current × Resistivity ÷ Area

The calculation uses a copper resistivity of approximately 0.017241 Ω·mm²/m and an aluminum resistivity of approximately 0.028264 Ω·mm²/m at a reference temperature near 20°C. Actual resistance normally rises as conductor temperature increases.

Understanding the results

Result	Meaning
Voltage drop	The estimated number of volts lost in the cable.
Percentage drop	Voltage loss expressed as a percentage of source voltage.
Voltage at load	The approximate voltage reaching the connected equipment.
Power loss	Electrical power converted into heat within the conductor.
Circuit resistance	The estimated resistance used in the voltage-drop calculation.

How to use this calculator

Select the circuit

Choose DC, single-phase AC, or three-phase AC.

Enter electrical values

Add source voltage, load current, and one-way cable length.

Choose the conductor

Select copper or aluminum and specify its AWG or mm² size.

Review the result

Compare the calculated loss with your maximum allowed percentage.

Ways to reduce voltage drop

Use a conductor with a larger cross-sectional area.
Reduce the cable run where practical.
Use parallel conductors where codes and design permit.
Check connections for corrosion, damage, or looseness.
Keep conductor temperature and installation conditions in mind.

Frequently asked questions

Learn more about wire length, conductor sizing, acceptable voltage loss, and calculation accuracy.

Enter the one-way distance from the electrical source to the load. The calculator automatically accounts for the outgoing and return conductors in DC and single-phase circuits.

A 3% target is commonly used for planning individual branch circuits, but the correct limit depends on the installation, equipment requirements, and applicable electrical rules.

Yes. A cable with a larger cross-sectional area has lower resistance, which normally reduces voltage loss and conductor heating for the same current and distance.

Aluminum has higher electrical resistivity than copper. Therefore, an aluminum conductor generally needs a larger cross-sectional area to achieve similar resistance and voltage-drop performance.

No. Voltage-drop calculations and cable ampacity calculations are different. The selected cable must also be checked for current capacity, insulation rating, ambient temperature, grouping, installation method, and local code requirements.

Yes. Conductor resistance increases as temperature rises. This calculator provides a useful planning estimate using reference resistivity values, while actual field loss may be higher.