Most cable estimators online pretend to know your house: pick “3-bed semi” and they invent a number. This cable length planner refuses to guess. You enter each circuit the way an electrician actually walks it — how many points (sockets, data drops, lights) and the real routed distance per run, paced or taped by you — and it multiplies, adds your slack allowance for the drops, bends and terminations that tape measures forget, and totals the cable per circuit and overall, with roll counts at the drum size you buy. The numbers are only as honest as your tape measure, which is exactly the standard a real order should meet.
The worked example in the tool
Living room sockets: 6 points at 8 m average routed distance = 48 m of runs. Kitchen sockets: 4 points at 6 m = 24 m. Raw total: 72 m. At the 15% slack allowance the tool opens with, those become 55.2 m and 27.6 m — a total of 82.8 m, which is one 100 m roll with a sensible offcut, or a shortfall story if you had bought a 75 m roll on the raw figure. That gap between 72 and 82.8 is where real installations live: every point consumes cable going down the wall to it and a tail for termination, and no routed path is the straight line on the plan.
Measuring distances the way cable runs
Measure along the route, not through the air: from the distribution board up to ceiling level, across, and down to the point, because that is the path the cable physically takes. Where runs share a route (six sockets daisy-chained along one wall), the honest entry is the chain’s total routed length as one “run” rather than six guesses at the board distance — the planner multiplies points × distance, so model a chain as 1 point at the chain length, or enter each leg. For ring circuits, the run is the whole ring out and back to the board. Average distances are fine across identical rooms; they are a lie across a house with one long outlier run — give the outlier its own row.
The slack percentage
Slack pays for four things: vertical drops your floor-plan distances ignore, the sweep of bends (cable does not turn right angles), termination tails at both ends of every run, and the mistake you cut off and re-strip. Ten percent covers tidy work in stud walls with measured routes; 15% is the standard planning figure; 20–25% for conduit pulls, masonry chases measured from plans, or first-fix work where the board position is not final. Slack is bought once; a second drum bought mid-job costs a delivery and a day.
Scope — planning, not design
This planner totals length only. It does not size cable: conductor cross-section, voltage drop over long runs, circuit protection and grouping are design decisions governed by your wiring regulations, and they can change which cable you buy in ways no length tool can see. It also treats each circuit independently — shared containment, fire stopping and segregation are installation questions. What it does settle is the purchase quantity from your own measurements: the number that keeps the last point of the last circuit from waiting on a second roll.
One drum or several?
The roll count hides a practical choice. A single 100 m drum of one cable type is cheaper per metre than smaller rolls, but only if every circuit genuinely uses that type: lighting circuits and socket circuits often take different cross-sections, and a drum of the wrong cable is not a saving. Split the plan by cable type — one set of rows per type, one run of this planner each — whenever the installation mixes them. The totals then read as a shopping list per drum, which is how the merchant will sell it to you anyway. Keep the offcuts labelled by circuit when the job ends: in two years, the person troubleshooting a dead socket will be glad the tails in the board are honest.
Related tools
Versión en español: Calculadora de Metros de Cable Eléctrico por Circuito: Puntos, Distancias y Margen de Holgura · Baseboard Calculator · Cable Metres per Room Estimator (in Spanish).
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