Cable Length Calculator — Estimate Total Cable Needed

This calculator estimates the total cable length needed for a circuit by adding up the distance from the consumer unit to the first outlet, the spacing between subsequent outlets, termination allowances at each connection point, and an optional wastage factor.

The formula

Total cable = (CU to first outlet + spacing between outlets) + termination allowances + wastage

Breakdown

• Run length: Distance from consumer unit to first outlet, plus the spacing between all subsequent outlets
• Ring return leg: For a ring final circuit (Ring toggle on), the cable returns to the same protective device, so a return leg from the last outlet back to the consumer unit is added (BS 7671 Reg 433.1.204)
• Termination allowance: 300mm per connection point (the consumer unit plus each outlet) for stripping, terminating, and neat connection — an estimating convention, not a BS 7671 figure
• Wastage: ~10% extra for cutting waste, measurement errors, and route changes (optional; a rule of thumb rather than a standard)

Choose radial (cable ends at the last outlet) or ring final(cable loops back to the consumer unit) with the circuit-type toggle. For accurate results, measure the actual cable route including vertical drops, horizontal runs through joists, and any detours around obstacles. The calculator works for any cable type — twin and earth, SWA, or flexible cable.