All free tools
Electrical Engineering
Cable Size & Voltage Drop Calculator
Enter your load and run length — get the correct copper conductor size with current rating and voltage drop checked side by side, for single and three phase circuits.
5% is the common limit for final circuits; use 2.5% for motors and sensitive equipment.
Recommended copper conductor
4 mm²
32.0 A load · 10.6 V drop (4.6%) over 30 m
Copper conductor comparison — your load on every size
| Size | Rating | Volt drop | % | Verdict |
|---|---|---|---|---|
| 1.5 mm² | 17.5 A | 27.8 V | 12.1% | Over current |
| 2.5 mm² | 24 A | 17.3 V | 7.5% | Over current |
| 4 mm² | 32 A | 10.6 V | 4.6% | ✓ Recommended |
| 6 mm² | 41 A | 7.0 V | 3.0% | OK |
| 10 mm² | 57 A | 4.2 V | 1.8% | OK |
| 16 mm² | 76 A | 2.7 V | 1.2% | OK |
| 25 mm² | 101 A | 1.7 V | 0.7% | OK |
| 35 mm² | 125 A | 1.2 V | 0.5% | OK |
| 50 mm² | 151 A | 0.9 V | 0.4% | OK |
| 70 mm² | 192 A | 0.6 V | 0.3% | OK |
| 95 mm² | 232 A | 0.4 V | 0.2% | OK |
| 120 mm² | 269 A | 0.3 V | 0.2% | OK |
| 150 mm² | 309 A | 0.3 V | 0.1% | OK |
| 185 mm² | 353 A | 0.2 V | 0.1% | OK |
| 240 mm² | 415 A | 0.2 V | 0.1% | OK |
| 300 mm² | 477 A | 0.1 V | 0.1% | OK |
Guide values for PVC-insulated copper, clipped direct, 30 °C ambient. Grouping, conduit, high ambient and aluminium conductors change ratings — final selection is confirmed by our engineers to SANS 10142 / your site standard.