cable voltage drop calculator

If you are sizing power cables for a home workshop, industrial panel, solar system, or EV charger, voltage drop matters. Too much drop means equipment runs at a lower voltage than intended, motors overheat, lights dim, and efficiency falls. Use the calculator below to estimate cable voltage drop quickly and decide if you should increase conductor size.

System Type

Conductor Material

Cable Length (one-way, meters)

For single-phase/DC, return path is included automatically in the formula.

Load Current (A)

Conductor Cross-Section (mm²)

System Voltage (V)

Conductor Temperature (°C)

Resistance is corrected from 20°C using a standard temperature coefficient.

What Is Cable Voltage Drop?

Voltage drop is the reduction in voltage along a cable caused by conductor resistance. As current flows through a wire, some electrical energy is converted into heat. The longer the run, the higher the current, and the smaller the conductor size, the larger the drop.

In practical design, keeping voltage drop low helps maintain equipment performance and improves energy efficiency. Many designers target around 3% or less for branch circuits and under 5% total from service to load, depending on local code and application requirements.

How This Calculator Works

Inputs Used

System type: DC/single-phase or three-phase
Material: Copper or aluminum (different resistivity)
Length: One-way cable length in meters
Current: Load current in amps
Cable area: Conductor area in mm²
Voltage: Nominal supply voltage
Temperature: Adjusts resistance above/below 20°C

Core Formula

Resistance of one conductor: R = ρ × L / A

Single-phase/DC drop: V_drop = 2 × I × R

Three-phase drop: V_drop = √3 × I × R

Percent drop: %Drop = (V_drop / V_system) × 100

This model estimates resistive drop only. For very long AC runs, harmonic-rich systems, or precision design work, include reactance and power factor in a full engineering calculation.

How to Use the Results

After clicking Calculate Voltage Drop, you get:

Voltage drop in volts
Voltage drop as a percentage
Estimated receiving-end voltage
Approximate cable power loss in watts
Suggested minimum cable area for a 3% target

Design Tips to Reduce Voltage Drop

Increase cable cross-sectional area
Use copper if feasible (lower resistivity than aluminum)
Reduce cable run length by moving distribution points closer to loads
For high-power loads, use higher system voltage where practical
Group loads and improve distribution architecture instead of one long feeder

Example Scenario

Suppose you have a 30 m one-way single-phase run, 25 A load, 6 mm² copper, and 230 V supply. You may see roughly a 2% drop, which is often acceptable for general circuits. If the same run used a smaller conductor (say 2.5 mm²), the drop would climb significantly and might exceed recommended limits.

Important Notes

This tool is for quick estimation and planning.
Always verify against your local electrical code and installation standards.
Cable grouping, insulation type, ambient heat, conduit fill, and installation method also affect final conductor sizing.
For mission-critical systems, have a licensed electrical engineer review the design.