What is the maximum voltage drop allowed?

IEC and most national codes recommend a maximum of 3–5% voltage drop from the supply point to the load. A 3% limit is common for lighting circuits; 5% is typical for power circuits. Critical equipment often requires 2% or less.

Why is the cable length entered one-way?

The calculator multiplies the one-way length by 2 (or by √3 for three-phase) internally to account for the full conductor length the current must travel through the circuit. Enter only the distance from source to load.

Copper or aluminum — which should I choose?

Copper has lower resistivity and is easier to terminate, making it the default for most installations. Aluminum is lighter and cheaper for large cross-sections (95 mm² and above) but requires larger cross-sections to match copper performance and needs anti-oxidant compounds at terminations.

Does this calculator account for cable ampacity (heating)?

This tool calculates the cross-section required for voltage drop only. You must also verify that the selected cable size meets the current-carrying capacity (ampacity) rating for the installation method and ambient temperature as per your local standard (e.g., IEC 60364, NEC 310).

What standard cable sizes are used?

Results are rounded up to the nearest IEC 60228 preferred cross-sections: 1, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240, 300, 400, 500, 630 mm².

Can I use this for DC circuits?

Yes. Select "DC" as the circuit type. The calculator uses a two-conductor DC model (both positive and return conductors carry the full current), so the voltage drop formula uses 2 × length × current × resistivity / cross-section.

Cable Size Calculator

Name: Cable Size Calculator
Availability: InStock
Author: Nham Vu

Calculate the minimum cable cross-section (mm²) needed for your load current, run length, and acceptable voltage drop.

Cable Parameters

Load Current (A)

One-Way Cable Length (m)

System Voltage (V)

Circuit Type

Single-phase Three-phase DC

Conductor Material

Copper Aluminum

Max Voltage Drop (%)

IEC recommends 3% for lighting, 5% for power circuits.

Enter your parameters and click Calculate.

Recommended Cable Size

mm²

Minimum calculated: mm² — rounded up to nearest IEC 60228 standard size.

Voltage Drop

% of supply

Power Loss

I²R losses in cable

Cable Resistance

mΩ

Total loop resistance

Effective Length

Total conductor length

Voltage Drop by Standard Cable Size

Size (mm²)	V Drop (V)	V Drop (%)

Summary

Calculate the minimum cable cross-section (mm²) needed for your load current, run length, and acceptable voltage drop.

How it works

Enter the load current (amps) and one-way cable length (meters).
Choose the conductor material: copper (resistivity 0.0175 Ω·mm²/m) or aluminum (0.028 Ω·mm²/m).
Select the circuit type: single-phase AC, three-phase AC, or DC.
Set the system voltage and maximum allowable voltage drop percentage.
The calculator solves for the minimum cross-section using Ohm's law and voltage-drop equations, then rounds up to the nearest IEC standard cable size.
Results show voltage drop (V and %), power loss (W), and the recommended standard cable size.

Use cases

Sizing supply cables for motors, pumps, and industrial equipment.
Designing domestic and commercial electrical installations to meet wiring regulations.
Calculating long cable runs in solar PV systems and EV charging circuits.
Verifying that existing wiring meets voltage drop limits before adding new loads.
Estimating cable costs by comparing copper vs. aluminum options.
Checking compliance with NEC, IEC, or AS/NZS voltage-drop limits.

Frequently Asked Questions

Related tools

Voltage Drop Calculator Wire Gauge Calculator Three Phase Power Calculator

Last updated: 2026-05-23 · Reviewed by Nham Vu