Cable Count Calculator
Count fabric and access cables for a leaf-spine build, including a spares allowance.
Inputs
Cables to Order
1,549cables
Leaf-to-Spine Cables
128cables
Server Access Cables
1,280cables
Spare Cables Included
141cables
Cables in Service
1,408cables
Step by step
Values used
Leaf switches = 16 switches; Spine switches = 4 switches; Links between each leaf and spine = 2 links; Servers per leaf = 40 servers; NIC ports per server = 2 ports; Spares allowance = 10 %
Cable Count
fabric cables = leaves × spines × links per pair; access cables = leaves × servers per leaf × NIC ports; add the spares percentage.
Cables to Order
= 1,549 cables
Leaf-to-Spine Cables
= 128 cables
Server Access Cables
= 1,280 cables
Spare Cables Included
= 141 cables
Cables in Service
= 1,408 cables
How it works
A full-mesh leaf-spine needs one cable from every leaf to every spine for each parallel link, which grows as the product of the two tiers. Access cabling is per NIC port, and a 10% spares allowance covers breakage and moves. Cabling is often the largest single line item and the longest lead time in a fabric build, and a recount after installation starts is expensive.
Formula
Cable Count
fabric cables = leaves × spines × links per pair; access cables = leaves × servers per leaf × NIC ports; add the spares percentage.
- links per pair
- Parallel cables between one leaf and one spine
- spares
- Allowance for damaged, mislabelled and future cables
Frequently Asked Questions
How is Cable Count calculated?
fabric cables = leaves × spines × links per pair; access cables = leaves × servers per leaf × NIC ports; add the spares percentage. A full-mesh leaf-spine needs one cable from every leaf to every spine for each parallel link, which grows as the product of the two tiers. Access cabling is per NIC port, and a 10% spares allowance covers breakage and moves.
Why does Cable Count matter?
Cabling is often the largest single line item and the longest lead time in a fabric build, and a recount after installation starts is expensive.
What values do I need to enter?
This calculator takes 6 inputs: Leaf switches, Spine switches, Links between each leaf and spine, Servers per leaf, NIC ports per server, Spares allowance. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.