Cable Size Calculator
Metric cable sizing in mm² for international solar installations. Enter current, distance, and voltage — get the right IEC cable size.
How to Use This Calculator
Enter current in amps and one-way distance in meters
Input the maximum continuous current in amps and the one-way cable run from source to load in meters. The calculator uses 2× the one-way distance as the complete circuit (cable runs out and returns). For solar strings, use your panel Isc × 1.25. For AC circuits, use rated load current × 1.25.
Set voltage and maximum voltage drop
Enter the system voltage and select your acceptable voltage drop. For DC solar circuits, 2% is the IEC 60364 recommendation. For AC branch circuits, 3% is typical. The lower the allowable drop, the thicker (and more expensive) the cable.
Results include AWG equivalent
The result shows the recommended IEC standard cable size in mm², plus the nearest AWG equivalent — useful if you're sourcing from a US supplier or working on a system that mixes metric and imperial specs.
The Formula
Standard IEC cable sizes follow the R10 geometric series: 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120 mm². Each step up reduces resistance by roughly 37% and increases current capacity proportionally. The resistance values used are for copper conductors at 20°C per IEC 60228.
Example
Solar array to inverter — 15m run, 24V system
A 24V solar system produces 18A through a 15-meter cable run to an inverter. Maximum acceptable voltage drop is 2%.
Result
This 24V, 15m run requires 25mm² cable. On a 48V system with the same power, current halves to 9A — and 10mm² cable would be sufficient. Again demonstrating why 48V systems need far less copper than 24V.