For everywhere the wire is sold in mm² and the runs are measured in meters — 230/400 V systems and DC, with a selectable 3% or 5% budget.
Vd = 2 × I × L × ρ / A single-phase, √3 replacing 2 for three-phase — with L in meters, A in mm², and resistivity ρ ≈ 0.0225 Ω·mm²/m for copper (0.036 aluminum) at operating temperature. Percentage drop is Vd / Vnominal × 100.
National rules differ in the limit, not the physics: the UK uses 3%/5% (BS 7671), Australia/NZ 5% total (AS/NZS 3000), and IEC 60364-5-52 suggests 4% as a default where no national value applies. Pick the budget that matches your jurisdiction.
| I | load current, amps |
| L | one-way length, meters |
| ρ | resistivity ≈ 0.0225 Ω·mm²/m copper at operating temp |
| A | conductor cross-section, mm² |
Equivalent to the tabulated mV/A/m method: the two-core table value is exactly 2ρ/A × 1000. √3 replaces 2 for three-phase line values.
Use your national wiring rules: 3% lighting / 5% power in the UK, 5% total in AU/NZ, 4% as the IEC default elsewhere. When in doubt, 3% is a safe design target.
Yes — select a DC system voltage and the tool uses the same 2× round-trip factor with your chosen percentage budget.