Electrical Cable Length Calculator - Metres by Cross-Section

The problem with estimating cable

Ordering cable for a rewire typically goes one of two ways. Buy too little and the electrician stops mid-job waiting for a delivery. Buy too much and you are left with expensive offcuts that never get used. The root cause is the same: nobody counts the metres circuit by circuit. This calculator fixes that. You enter the number of lighting, outlet and dedicated circuits, the average run length from the distribution board, and a waste percentage. It splits the result by cross-section - 1.5 mm2 for lighting, 2.5 mm2 for outlets, 4-6 mm2 for dedicated appliances and 10 mm2 for the main feed - so you can order each size separately.

The solution: circuit-by-circuit breakdown

Without calculation

"I need about 200 m of cable for the house" - bought as a single roll of 2.5 mm2. Result: no 1.5 mm2 for lights, no 4 mm2 for the oven, second trip to the supplier, downtime.

With this calculator

"I need 48 m of 1.5 mm2, 86 m of 2.5 mm2, 28 m of 4 mm2 and 12 m of 10 mm2" - each size ordered separately, 15% waste included, no surprises on site.

How to use this calculator - step by step

Building type - apartment, single-storey house, two-storey house or commercial. This sets a default main-feed length and adds vertical risers for multi-storey buildings.
Lighting circuits - number of separate B10A circuits on 1.5 mm2 cable. One circuit per 1-2 rooms.
Outlet circuits - number of B16A circuits on 2.5 mm2 cable. One per room group, separate for kitchen and bathroom.
Dedicated circuits - separate runs for oven, hob, boiler, AC, EV charger on 4-6 mm2 cable.
Average run length - distance from the distribution board to the typical point of use, measured along walls.
Waste allowance - 10-20% extra for junction-box tails, wall penetrations and cutting errors.
Meter-to-board distance - optional override for the main 10 mm2 feed cable.
Read results: metres per cross-section, material summary table, panel components and optional cost estimate.

Cable cross-sections and breaker ratings

Cross-section	Max current (A)	Breaker	Typical use
3x1.5 mm2	15.5	B10A	Lighting circuits
3x2.5 mm2	21	B16A	General socket outlets
3x4 mm2	28	B20A	Oven, boiler, AC unit
5x6 mm2	36	B32A	Induction hob, EV charger
5x10 mm2	50	C40A	Main feed (up to 14 kW)

Current ratings per IEC 60364 for cables installed in insulated walls (method A). Actual capacity depends on installation method, grouping and ambient temperature.

Typical cable quantities by building type

Building	3x1.5 mm2	3x2.5 mm2	3x4+ mm2	Total
Apartment 50 m2	30-40 m	50-70 m	15-25 m	100-140 m
Apartment 100 m2	50-70 m	80-120 m	25-40 m	160-230 m
House 120 m2 (1 storey)	60-90 m	100-150 m	30-50 m	200-300 m
House 180 m2 (2 storey)	90-120 m	150-200 m	40-70 m	300-400 m

Practical examples

Example 1: Two-bedroom apartment, 65 m2
3 lighting + 4 outlet + 2 dedicated circuits, avg run 5 m, 15% waste. Total: ~120 m (25 m of 1.5, 49 m of 2.5, 14 m of 4, 6 m of 10 mm2).

Example 2: Single-storey house, 130 m2
5 lighting + 7 outlet + 3 dedicated, avg run 8 m, 15% waste. Total: ~260 m (65 m of 1.5, 110 m of 2.5, 32 m of 4, 12 m of 10 mm2).

Example 3: Two-storey house, 180 m2
7 lighting + 9 outlet + 4 dedicated, avg run 10 m, 15% waste. Total: ~390 m (120 m of 1.5, 185 m of 2.5, 56 m of 4, 14 m of 10 mm2).

Example 4: Commercial unit, 200 m2
6 lighting + 8 outlet + 5 dedicated, avg run 12 m, 20% waste. Total: ~420 m (122 m of 1.5, 196 m of 2.5, 84 m of 4, 18 m of 10 mm2).

Example 5: Small apartment, 40 m2 (meter 3 m from board)
2 lighting + 3 outlet + 1 dedicated, avg run 4 m, 10% waste. Total: ~70 m (13 m of 1.5, 23 m of 2.5, 6 m of 4, 4 m of 10 mm2).

FAQ - Frequently asked questions

How many circuits does a typical house need?

A 120 m2 single-storey house typically needs 4-6 lighting circuits, 5-8 outlet circuits and 2-4 dedicated circuits (oven, hob, boiler, AC). The exact number depends on room count and appliances. Rule of thumb: max 10 light points per lighting circuit and max 10 sockets per outlet circuit.

Why not use 2.5 mm2 for everything?

Using 2.5 mm2 for lighting circuits wastes money - the thicker cable costs 40-60% more per metre than 1.5 mm2, and lighting loads are well within the 1.5 mm2 capacity. Going the other way is dangerous: running a 16A outlet on 1.5 mm2 cable exceeds its rated current and creates a fire risk.

What is the waste allowance for?

The allowance covers: cable tails entering and leaving junction boxes (15-20 cm each), spare loops left at switchboard for future modifications, waste from cutting to length, and extra length for routing around obstacles. Industry standard is 15%. Simple apartment jobs can use 10%. Complex houses with many wall penetrations: 20%.

Does a two-storey house need more cable than a bungalow of the same area?

Yes. About 50% of circuits serve the upper floor and each needs an extra ~3 m for the vertical riser from the ground-floor distribution board. On a 12-circuit house, that adds roughly 18-20 m of cable. The calculator handles this automatically when you select "Two-storey house".

How do I measure the average run length?

Pick a representative socket or light point and measure the cable path from the distribution board: down the wall, along the ceiling void or under the floor, through any wall penetrations, and up to the fitting. Do this for 3-4 points in different rooms and take the average. Typical values: apartment 3-6 m, single-storey house 5-10 m, two-storey house 6-12 m.

What about the main feed cable from the meter?

The main feed runs from the electricity meter (or connection point) to the distribution board inside the building. In an apartment this is typically 3-6 m. In a house with the meter at the property boundary it can be 10-30 m of armoured or buried cable. The calculator uses a sensible default per building type, but you can override it with the "Meter-to-board distance" field.

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