Cable Cross-Section Calculator
Enter the cable length, current, and allowed voltage drop to find the minimum copper cable cross-section needed.
Uses copper's resistivity of 0.0175 Ω·mm²/m.
How minimum cable cross-section is calculated
This calculator uses A = (2 × ρ × L × I) / ΔV, where ρ is copper's resistivity, L is the one-way cable length, I is the current, and ΔV is your allowed voltage drop. The length is doubled since current travels out to the load and back to complete the circuit.
This gives the theoretical minimum cross-section to stay within your voltage drop limit. In practice, you should round up to the next standard commercially available cable size, since cables aren't manufactured in arbitrary cross-sections.
Frequently asked questions
Why use mm² instead of AWG for cable size?
Square millimeters (mm²) is the standard cable sizing unit in most of the world outside North America, which commonly uses AWG (American Wire Gauge) instead. Both describe the same physical property — the wire's cross-sectional area — just in different units.
What voltage drop limit should I use?
Many electrical codes recommend keeping voltage drop under 3% of the circuit's nominal voltage for branch circuits, and under 5% total including the feeder — convert your percentage limit to an actual voltage value based on your system's voltage before using this calculator.
Should I round up to the next standard cable size?
Yes — cables are manufactured in standard sizes (like 1.5, 2.5, 4, 6, 10 mm², and so on), not arbitrary cross-sections. Always round your calculated minimum up to the next available standard size, never down.