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Patch cable length calculator

The patch cords have to be ordered before the install, and nobody wants to walk the row with a tape measure for every route. Guess too long and you're coiling metres of slack into the tray; guess too short and the cord stops 40 cm before the port. Enter both ports and the route: you get the length, how it's built up, and the standard length to order. Works for fiber patch cords, DAC, AOC and CAT6A.

Calculate the patch cable length for one route

Fiber with the transceiver ends built in. Longer than a DAC, still one piece from port to port.

Route

Up to the rack top, across the rack roofs, down into the other rack.

U1 is the bottom of the rack. 1U = 44.45 mm.

Optional: extra length through patch panel trays or horizontal cable managers.

2 rack(s) in betweenRack ARack B A (U40) B (U38)
Schematic. Heights to scale, horizontal distances not.

Calculated length

2.71 m

Vertical at A
0.11 m
Horizontal
1.80 m
Vertical at B
0.20 m
Slack (2 × 0.30 m)
0.60 m
Detours
0.00 m
Total
2.71 m

Next standard length of AOC SFP+ 10G

3 m (+0.29 m on top of the route)

Lengths from our catalog (snapshot); the live catalog didn't respond.

This is one route. SpanWise does the whole hall.

This calculator assumes a straight route between two racks you describe. SpanWise routes every patch along the real duct graph of your hall (trays, risers, crossings) and returns a patch list with the cut length for every cable. Built for the next migration, not for one cord.

How the calculation works

  1. Port height is the centre of its U: (U − 0.5) × 44.45 mm from the bottom of the rack.
  2. Vertical: from each port to the height where the cable crosses over. That's the highest port for the same or adjacent rack, the rack top for a run along the row, and the tray (rack top + tray height) for an overhead route.
  3. Horizontal: (racks in between + 1) × rack width, centre to centre. Zero within the same rack.
  4. Total: vertical A + horizontal + vertical B + detours + 2 × slack, then rounded up to the next length we stock.

It's a model of one straight route. Real halls have risers, crossings and cable managers that add length. Measure one representative route on the floor before you order a batch, and use the detours field for what the model doesn't see.

Frequently asked questions

How do you measure patch cable length in a data center?

Follow the path the cable will actually take, not the straight line between ports. From port A to where the cable leaves the rack, up to the cable tray or across to the next rack, along the route, and down to port B. Add the detours through cable managers and slack at both ends. That sum is exactly what this calculator does for one route.

What are standard fiber patch cable lengths?

No standard prescribes them: every supplier stocks fixed steps. Our OS2 LC-LC patch cords run from 50 cm to 35 m; OM3 and OM4 come in fewer steps. The calculator rounds up to the lengths in our catalog, so what you calculate is what you can order.

How much slack should a patch cable have?

Enough to re-seat a connector or move a port, not more. 0.3 m per end is a practical default. Excess slack ends up coiled in the tray, where it blocks airflow and makes tracing a cable harder. Whatever you coil, keep it above the cable's minimum bend radius.

What length do I need from patch panel to switch?

In the same rack it's short: the height difference between the two U positions, plus slack and the detour through the cable manager. A panel and switch a few U apart usually come out at 75 cm or 1 m with default slack. Pick 'Same rack' above and enter both U positions to check.

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