| Metric size (area per mm2) | Resistance per 100metres for 2 wires (ohms) |
| 1 | 4.2 |
| 2.5 | 1.5 |
| 4 | 0.92 |
| 6 | 0.62 |
| 10 | 0.37 |
| 16 | 0.23 |
| 25 | 0.135 |
| 35 | 0.105 |
Loss (watts) = amps2(squared) X Resistance (ohms)
or
w = I2 (current squared) X R (resistance in ohms)
Quoted allowable drop = no more than half an amp for a 12 volt system.