Fabric Bandwidth Calculator

Total spine capacity, bisection bandwidth and per-leaf share for a data centre fabric.

About Fabric Bandwidth Calculator

Every spine port terminates on a leaf, so the spine layer's aggregate port capacity is the ceiling on inter-leaf traffic. Bisection bandwidth halves that figure because traffic crossing an imaginary line through the fabric uses capacity on both sides. Bisection bandwidth is the number HPC and AI workloads are benchmarked against, and per-leaf capacity tells you whether adding leaves will starve the existing ones.

Formula

Fabric Bandwidth

spine capacity = spines × fabric ports per spine × port speed; bisection bandwidth is half of that.

bisection bandwidth: Capacity across the worst-case cut that splits the fabric in two
capacity per leaf: Spine capacity divided evenly across attached leaves

Worked example

With the default values below, Fabric Bandwidth Calculator returns Total Spine Capacity of 51,200. Change any input above and every figure here is recalculated in your browser.

Inputs used

Spine switchesaccepts 1–64 switches: 4 switches
Fabric ports per spineaccepts 1–512 ports: 32 ports
Fabric port speedaccepts 1–800 Gbps: 400 Gbps
Leaf switches attachedaccepts 1–512 switches: 24 switches
Usable utilisation targetaccepts 10–100 %: 80 %

Results

Total Spine Capacity: 51,200 Gbps
Bisection Bandwidth: 25,600 Gbps
Capacity per Leaf: 2,133.3 Gbps
Total Capacity: 51.20 Tbps
Usable at Target Utilisation: 40,960 Gbps

Step by step

1Values used
2Fabric Bandwidth
3Total Spine Capacity= 51,200 Gbps
4Bisection Bandwidth= 25,600 Gbps
5Capacity per Leaf= 2,133.3 Gbps
6Total Capacity= 51.20 Tbps
7Usable at Target Utilisation= 40,960 Gbps

Assumptions and limits

The result is derived only from the 5 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.

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

Frequently Asked Questions

How is Fabric Bandwidth calculated?

spine capacity = spines × fabric ports per spine × port speed; bisection bandwidth is half of that. Every spine port terminates on a leaf, so the spine layer's aggregate port capacity is the ceiling on inter-leaf traffic. Bisection bandwidth halves that figure because traffic crossing an imaginary line through the fabric uses capacity on both sides.

Why does Fabric Bandwidth matter?

Bisection bandwidth is the number HPC and AI workloads are benchmarked against, and per-leaf capacity tells you whether adding leaves will starve the existing ones.

What values do I need to enter?

This calculator takes 5 inputs: Spine switches, Fabric ports per spine, Fabric port speed, Leaf switches attached, Usable utilisation target. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.