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Train Formation Length Calculator

Work out train formation length instantly with clear inputs, formula shown and shareable results.

About Train Formation Length Calculator

Formation length is locomotive length plus wagons times length over couplers. It matters because passing loops, reception sidings and platforms have fixed lengths, and a train even slightly too long cannot be crossed or berthed, forcing splitting or a longer routing.

Formula

Train length

L = loco length + wagons x length over couplers; wagons that fit = (available - loco) / wagon length

Worked example

With the default values below, Train Formation Length Calculator returns Train length of 632.70. Change any input above and every figure here is recalculated in your browser.

Inputs used

Locomotive length
19.5 m
Number of wagons
42 wagons
Length over couplers per wagon
14.6 m
Available loop or platform length
750 m

Results

Train length
632.70 m
Margin against the available length
117.30 m
Wagons that fit
50 wagons
Assessment
Fits with 117.3 m spare

Step by step

  1. 1Values used
  2. 2Train length
  3. 3Train length= 632.70 m
  4. 4Margin against the available length= 117.30 m
  5. 5Wagons that fit= 50 wagons
  6. 6Assessment= Fits with 117.3 m spare

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Rail results are planning estimates only. Verify against the infrastructure manager's rule book, approved braking curves and applicable railway safety regulations.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Rail results are planning estimates only. Verify against the infrastructure manager's rule book, approved braking curves and applicable railway safety regulations.

Frequently Asked Questions

Why use length over couplers?

It is the actual space each wagon occupies in a formation, including the coupling gear, which is what the loop must accommodate.

Should I leave a margin?

Yes. Signal overlaps, stopping accuracy and shunt clearances mean a practical margin of 10-20 m is normally planned.

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