How to calculate cable metres per circuit and conduit
On site, the costly mistake is not the price per metre — it is under-ordering because you counted conduit length instead of conductors, or forgot the traveller. This guide explains how CableFlow turns each run into cable metres by section and conductor type.
What a “run” means in an electrical cable calculator
Each project row is one conduit (or path) with zone/description, circuit type, measured distance, and a conductor specification (“spec”). Distance is the path length in the conduit. Cable metres come from that distance and the spec composition — they are not the same as conduit metres when multiple conductors are present or when the traveller is doubled.
That gives installers a reliable purchase list: metres of brown phase at 2.5 mm², blue neutral, grey traveller (VJ), and so on, aggregated across the project.
Automatic section by circuit type (I / T / P / S / Q / G)
In CableFlow you do not pick mm² manually in the cable table. You pick a circuit type, and the app maps the section used in summaries:
| Type | Typical use in the app | Section |
|---|---|---|
| I | Lighting | 1.5 mm² |
| T | Sockets | 2.5 mm² |
| P | Power | 4 mm² |
| S | Power 6 mm² | 6 mm² |
| Q | Large power | 10 mm² |
| G | Main feed | 16 mm² |
These values are the app’s internal table (see also FACTS_TO_VERIFY.md). On a real job, always confirm the section required by the electrical design and applicable rules — the calculator organises metres; it does not replace the design.
Conductor specs: FTN, F2R, 2VJTN and friends
Spec grammar is a sequence of [quantity?][code]. Quantity defaults to 1. Codes: F, R, VJ, N, T, C (longest match first so VJ is not read as V+J).
FTN→ 1×F, 1×T, 1×NF2R→ 1×F, 2×R2VJTN→ 2×VJ, 1×T, 1×NC→ 3-core multifilar cable (counts as 3 conductors for conduit fill; sold/measured as cable metres, not ×3)
UI colour swatches help review: F brown, R orange, VJ grey, N blue, T green/yellow, C black — an app convention, not a claim of mandatory colour mapping in every region.
The metres formula (and VJ ×2)
For each conductor in the spec:
metres = quantity × run distance × factor
Factor is 1 for most codes. VJ (traveller) always uses ×2: on an 8 m run with 2VJTN, VJ metres are 2 × 8 × 2 = 32 m, while T and N are 8 m each. That avoids the classic shortage of grey on two-way switching.
The project summary aggregates metres by section × conductor code. That aggregation later feeds the quote (purchase totals, not room labels).
Worked example
Zone “Hall”, type T (2.5 mm²), distance 12 m, spec FTN: F = 12 m, T = 12 m, N = 12 m — 36 m of cable for 12 m of conduit. A lighting run with 2VJ at 10 m (type I, 1.5 mm²) yields VJ = 40 m at 1.5 mm². The summary keeps sections separate for correct purchasing.
On-site habits
- Measure the real conduit path, not only plan distance.
- Keep zone naming consistent for review.
- Double-check VJ specs for the ×2 factor before ordering.
- When the list is stable, create the quote from the project instead of retyping metres.
Next
Continue with quoting from a cable list, margin vs markup, or the free calculator.