Fabric Bandwidth Calculator
Total spine capacity, bisection bandwidth and per-leaf share for a data centre fabric.
Inputs
Total Spine Capacity
51,200Gbps
Bisection Bandwidth
25,600Gbps
Capacity per Leaf
2,133.3Gbps
Total Capacity
51.20Tbps
Usable at Target Utilisation
40,960Gbps
Step by step
Values used
Spine switches = 4 switches; Fabric ports per spine = 32 ports; Fabric port speed = 400 Gbps; Leaf switches attached = 24 switches; Usable utilisation target = 80 %
Fabric Bandwidth
spine capacity = spines × fabric ports per spine × port speed; bisection bandwidth is half of that.
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
How it works
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
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.
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