Help & FAQ

Everything you need to plan precise patch cable runs across racks and cabinets using the calculator at cable.dvdp.co.uk.

Pro tip: allow a safety margin beyond calculated lengths to account for routing, bends, and cable management. A common practice is +10–15% extra per run.

Quick start

Open the calculator and set your rack height (U), number of cabinets, and cabinet spacing.
Choose your switch type (chassis or independent) and define patch panel layout (port ranges left/right as needed).
Set your preferred slack per run and any routing offsets if applicable.
Enter connections via Manual input or paste a list with Bulk input.
Review calculated lengths, then save or export your results.

Key concepts

Rack Unit (U)

Standard height measure for rack equipment. 1U = 4.5CM. Accurate U positions ensure realistic cable path lengths.

Cabinet Spacing

Distance between cabinets that cables must traverse. Include vertical and horizontal pathways and management hardware.

Port exit / entry side

Define which side ports are cabled from (e.g., ports 1–12 left, 13–24 right). This affects routing distance and calculated length.

Slack per run

Extra cable length added to each run to allow for service loops, dressing, and future moves/changes.

Field reference

This section breaks down each major field and how it affects calculations.

Field	What it means	Tips
Rack height (U)	Total height of each rack.	Ensure values are entered correctly for their relative cabinets.
Number of cabinets	How many racks/cabs are in the row.	Ensure each rack is named as per documentation.
Cabinet spacing	The distance between the inside of the vertical rail strip between cabinets.	Measure from the inside of the rail strip rather than just the cabinet's frame edges.
Switch type	Chassis vs independent switches.	Chassis Switch - Stack of switches. Independent Switch - 1U Switch
Port exit side (panel)	Left/right grouping of patch panel port pathways.	To ensure that the completed patching looks tidy and is easy to maintain.
Port entry side (switch)	Cabling entry side on the switch.	To ensure that the completed patching looks tidy and is easy to maintain.
Slack per run	Extra length added to each run.	Atleast 15cms/6inches or 10% recomended
Routing offsets	Additional vertical/horizontal allowances.	Use for unusual/nonstandard situations.

Examples

Single rack, one switch

24‑port panel at 20U → switch at 36U, ports 1–12 left.

Set rack height to match on-site (e.g., 42U).
Cabinets: 1. Spacing: 0.
Slack: 10-20cms / 4/8" per run.
Connect PP‑A:1‑12 → SW1:1‑12 (left exit).

Two cabinets, independent switches

PP‑A in Cab1 (18U) → SW2 in Cab2 (30U), spacing 0.8 m.

Cabinets: 2. Spacing: 0.8 m.
Ports 1–12 left; add +15% slack.
Use bulk input for 24+ runs.

Chassis switch with modules

Chassis at 28U with 4× line cards.

Define chassis U block and module groupings.
Set entry side per module if supported.
Export results for BOM aggregation.

Step-by-step guide

Follow these steps to build out a project from scratch.

Manual input

Under Layout, set rack height, cabinets, and spacing.
Configure Switches: choose chassis vs independent, define U positions, and entry side preferences.
Configure Patch Panels: set panel U positions and port groupings (left/right).
Open Connections, then add each run: select source panel/port and destination switch/port.
Review each calculated length; adjust slack per run if needed for site conditions.

Bulk input

Paste a CSV-like list to add many connections at once. Example format:

"Rack, Panel-U, Port, Switch, Blade, Port"
03-A01	42	18	03-012	DB6FBX03001	1	24
03-A02	23	5	03-069	DB6FBX03002	5	14
03-A01	42	11	03-111	DB6FBX03002	9	36

CSV rules:

Header row required as shown above (case-insensitive).
Names must match existing panels/switches exactly.
U values are integers; ports are 1‑based.
VLANS are optional and exported unchanged.

Saving & export

Save locally: store your project in the browser to return later.
Export JSON: download a portable config file to version-control or share.
Export results: download a CSV/Excel of runs and lengths for procurement and labeling.

Best practices

Slack Aim for +10–15% slack; increase when routing through busy verticals/horizontals.
Labeling Keep a consistent scheme: CAB‑RACK‑PANEL:PORT → SW:PORT.
Bend radius Respect minimum bend radius; add offset if routing is tight.
Test Plan spare runs for critical paths; export BOM with 3–5% spares.

FAQ

How accurate are the calculated lengths?▸

The calculator accounts for U positions, cabinet spacing, exit/entry sides, and slack. Real-world routing varies with management paths and bend radii; we recommend adding a 10–15% safety margin.

What does “slack per run” actually do?▸

It adds the specified length to each calculated run to allow for service loops and dressing. You can tune this per site—larger cabinets and denser cable trays may need more slack.

How do port exit/entry sides affect the result?▸

Ports exiting left vs. right change the horizontal travel needed before the cable drops or rises, impacting total length. Grouping by ranges (e.g., 1–12 left) mirrors real panel labeling.

Can I work across multiple cabinets?▸

Yes. Set the number of cabinets and spacing. The calculator adds inter-cabinet distance to runs crossing between frames.

Does the tool support chassis switches?▸

Yes. Define the chassis bottom U position and module port groupings; you are also able to mix chassis switches with independent switches in the same project.

How do I import/export a configuration?▸

Use Export to download a JSON file of your layout and connections. Use Import to load it later or share with a teammate. Results can also be exported as CSV/Excel.

Nothing happens when I click a port—what am I missing?▸

Check that required context is defined: panel names, switch names, U positions, and that the relevant mode is selected. If issues persist, reload the page and try a different browser.

What cable type should I order?▸

That depends on performance needs and environment. For general enterprise switching, Cat6 or Cat6A patch leads are common. For longer inter-cabinet trunks consider pre-terminated Cat6A or fiber depending on bandwidth and distance.

Can I mix fiber and copper in one project?▸

Yes. Plan fiber trunks separately with appropriate transceivers and patch leads. Note different minimum bend radii and consider allowing for more slack when using fiber.

Troubleshooting

Incorrect lengths? Re-check U positions and exit/entry side settings; ensure cabinet spacing is accurate.
Bulk import mismatches? Confirm consistent naming (e.g., SW1 vs Sw1) and column order.
Stuck on processing? Try a fresh tab and disable heavy extensions; clear local saves if corrupt and re-import JSON.
Printing looks off? Use your browser’s print dialog; this page includes a print-friendly stylesheet.

If problems continue, export your JSON and share it via the contact method below.

Glossary

U (Rack Unit): 4.5cm standard height increment for rack equipment.

Service loop: Extra cable length coiled for maintenance or re-termination.

Patch panel exit side: The side of a panel where patch leads are dressed into cable managers.

Chassis switch: A modular switch with line cards; behaves as a single device with multiple port groups.

Independent switch: A standalone switch; each device has its own U position and entry side.

Contact

Questions, bugs, or ideas? let me know by contacting me at dvanderpijll@align.com.