House Rewiring Calculator — Circuits, Cable & Consumer Unit

This calculator estimates the electrical requirements for a full house rewire based on property type, size and additional requirements. It uses typical UK domestic installation practices and BS 7671 18th Edition guidelines.

Base specification (3-bed semi)

• Ring mains: 2 (ground floor + first floor)
• Lighting circuits: 3 (one per floor plus the landing)
• Cooker circuit: 1 (6mm² T&E, 32A MCB)
• Smoke-alarm supply: 1 dedicated way for the interlinked BS 5839-6 system
• Consumer unit: circuits + your chosen spare ways (default 2); a bare 3-bed comes to ~9 ways, rising to 11-13 once an electric shower, EV charger or other dedicated circuits are added
• 2.5mm² cable: ~150m (sockets)
• 1.5mm² cable: ~100m (lighting)

Adjustments

• Additional bedrooms and floors increase circuit count and cable length
• Electric shower adds a dedicated 40/45A circuit and ~15m of 10mm² T&E
• EV charger adds a dedicated 32A radial (standard 7kW home charger). The cable is 6mm² T&E up to roughly 30m; the result steps up to 10mm² for longer runs. The 30m step-up reflects the more onerous of two BS 7671 limits — voltage drop (6mm² = 7.3 mV/A/m, Table 4D5; the 5% / 11.5V limit is reached near 49m but good practice keeps an EV charger nearer 3%) and current-carrying capacity once the cable runs through wall voids or thermal insulation (Reference Method 101/102, Section 722), where 6mm² derates well below its 47A clipped-direct rating
• Underfloor heating and smart home systems add dedicated circuits

Smoke detectors (BS 5839-6)

A rewire triggers minimum Grade D LD2 requirements: mains-powered, interlinked smoke alarms in every circulation space (hallways and landings), a heat alarm in the kitchen, and an alarm in the principal habitable room. The detector count shown here is an indicative minimum based on floor count — confirm it against the actual circulation spaces and high-risk rooms in your property, as LD2 is driven by layout, not a fixed multiple of floors.