Conduit and Wiring Calculator
Conduit, wire and copper weight per circuit, all at once.
Quick answer
With the default inputs: Circuits 10 circuits · Average run per circuit 25 m · Wires per conduit 3 pcs etc.Total wire length 825 m
Edit the inputs below to recalculate.Inputs
Result
Total wire length
825m
| Conduit net length | 250.0m |
| Conduit with waste | 262.5m |
| Wire net length | 750m |
| Wire with allowance | 825m |
| Copper per metre | 0.0222kg/m |
| Total copper weight | 18.4kg |
| Coils at 100 m | 9coils |
| Wire per circuit | 82.5m |
This is a circuits × average-run estimate for early design and procurement; final quantities must be measured from drawings. Conductor size affects weight only — ampacity and voltage drop are not checked here and must be calculated separately from design current, installation method, ambient temperature and allowable drop. 1.5 mm² lighting and 2.5 mm² socket circuits are conventional but not transferable to heavy loads. Copper is taken at 8.9 g/cm³ excluding insulation, which adds about 10-15% for BV cable.
Formula
| Conduit net length | L = circuits × average run |
| Conduit total | L = net × (1 + conduit waste) |
| Wire net length | L = conduit net × wires per conduit |
| Wire total | L = net × (1 + allowance) |
| Copper weight | W = total length × area(mm²) × 8.9 ÷ 1000 |
10 circuits at 25 m each, 3 × 2.5 mm² per conduit: 250 m net conduit, 262.5 m with 5% waste; 750 m net wire, 825 m with 10% allowance; 18.4 kg of copper, nine 100 m coils.
FAQ
How many wires fit in one conduit?
Total conductor cross-section including insulation must stay under 40% of the conduit bore — that keeps pulling feasible and heat dissipation adequate. Practically, PVC20 has roughly a 16 mm bore and 201 mm² area, so 80 mm² is the limit; BV2.5 is about 4.2 mm overall and 13.9 mm², allowing five at most and three to four in practice. Overfilling makes pulling impossible and re-wiring later hopeless.
Why and how much wire allowance?
Terminations need slack. Each conductor in a panel is left half the panel perimeter for dressing and terminating, boxes take 100-150 mm for joints, and expansion joints need compensation. The rule is half-panel-perimeter in cabinets and 150 mm in boxes, totalling 8-15% of run length — take the upper end for short runs with many enclosures. Without allowance the wire sits under tension and loosens with heat or vibration.
Why 1.5 mm² for lighting and 2.5 mm² for sockets?
Because the loads differ. A lighting circuit is small — often 10-20 luminaires under 1 kW — and 1.5 mm² copper in conduit carries about 14-16 A, sufficient and economical. Socket circuits feed kettles, hairdryers and air conditioners, where 2.5 mm² carries 19-22 A with a C16 or C20 breaker. Kitchens, air conditioning and instant water heaters need their own 4 or 6 mm² circuits. These sizes are a safety floor, not a place to economise.
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Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.