Add switch, serialisation, cable propagation and queueing delay to get end-to-end fabric latency.
Cut-through switches contribute a fixed sub-microsecond delay per hop, propagation adds 5 ns per metre of fibre, and serialisation is the packet clocking out at line rate. Faster ports shrink serialisation dramatically — a 1500-byte frame takes 12 µs at 1G but only 0.12 µs at 100G. Storage, RDMA and distributed databases quote latency budgets in microseconds, and this breakdown shows whether hops, cable runs or queueing is the part worth engineering.
Network Fabric Latency
latency = hops × switch latency + hops × cable metres × 5 ns/m + hops × serialisation + queueing, where serialisation = packet bits ÷ port speed.
latency = hops × switch latency + hops × cable metres × 5 ns/m + hops × serialisation + queueing, where serialisation = packet bits ÷ port speed. Cut-through switches contribute a fixed sub-microsecond delay per hop, propagation adds 5 ns per metre of fibre, and serialisation is the packet clocking out at line rate. Faster ports shrink serialisation dramatically — a 1500-byte frame takes 12 µs at 1G but only 0.12 µs at 100G.
Storage, RDMA and distributed databases quote latency budgets in microseconds, and this breakdown shows whether hops, cable runs or queueing is the part worth engineering.
This calculator takes 6 inputs: Switch hops, Latency per switch, Cable length per hop, Packet size, Port speed, Queueing delay budget. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.