Cable cross-section
Conservative AC/DC mm² from voltage drop and heating. Default example: 12 V DC, 5 A, 5 m one-way copper at 3% drop → 4 mm² (≈ 11 AWG).
Can be added as standalone app and used offline. Not a substitute for an electrician or national wiring rules.
On iPhone or iPad: Share → Add to Home Screen.
4 mm²
≈ 11 AWG
Voltage drop is the limiting check.
This calculator picks a conservative copper mm² from voltage drop and heating. Length is one-way metres. It is not a wiring design — have an electrician check the circuit.
Copper at 3% drop: 4 mm² (≈ 11 AWG). Voltage drop governs; heating alone would allow 0.75 mm². That is the default example on this page (typical LED, pump, or similar extra-low voltage DC run).
At 12 V a few metres of cable eat a large share of the budget. The same 5 A load at 10 m one-way needs 10 mm² (≈ 7 AWG) for 3% drop — not because the wire is hot, but because the volts run out. Boat and van electrics often look “oversized” next to 230 V house cable. This page uses ISO 10133-style ELV DC ampacity plus voltage drop; bundling and ABYC/ISO marine rules can still require a larger size. In a marine environment use tin-coated (tinned) copper cable so the strands resist corrosion; the mm² size from this calculator is the same as for bare copper.
Same 5 A, 5 m, copper, 3%: 2.5 mm² (≈ 13 AWG). Doubling the voltage halves the relative drop, so the cross-section can be smaller. That is why 24 V is common on larger DC systems.
This tool matches IEC area to the nearest ASTM B258 conductor area (then kcmil above 4/0). 4 mm² → 11 AWG (4.17 mm²), not 12 AWG (3.31 mm²). It is an area equivalent, not an NEC ampacity size.
Copper, 1-phase, 3% lighting: 1.5 mm² (≈ 15 AWG). House circuits are usually limited by heating and national rules, not by voltage drop on a short run. Use Advanced settings for 5% “other” loads or 3-phase.
Yes for copper (or aluminium in Advanced), AC and DC. It also checks a conservative ampacity table and recommends the larger of the two sizes. Enter voltage, current, and one-way length; install the page on a PC, iPhone, or Android phone to use it offline.