How to calculate network latency
Build a path by adding switches, firewalls, fiber links and WAN connections in the order traffic passes through them. Latency Lens adds the selected delays and shows which components contribute most to your estimate. Use custom latency to include a delay that is not in the equipment list.
For a custom fiber segment, the calculator uses approximately 5 ns per meter. A custom WAN distance uses the equivalent 5 µs per kilometer. Both are propagation estimates for one direction; they do not automatically include equipment delays or a return trip.
Path estimate = sum of selected component delays
A worked network example
Suppose two switches each contribute an assumed 350 ns and the connecting fiber is 100 m long. The fiber contributes 500 ns, giving a path estimate of 350 + 500 + 350 = 1,200 ns, or 1.2 µs. The switch figures here are illustrative; actual latency depends on the equipment and its operating mode.
One-way latency and round-trip time
The total represents the components you add. Doubling a one-way estimate gives a round-trip estimate only when the return path and delays are equivalent. Check the definition of any published WAN figure before mixing it with other values.
ICMP (ping) is not a reliable way to measure very low forwarding latency. When you ping a network device itself, replies are often deprioritised and handled by its control-plane CPU, so measurements can be CPU-bound.
For a distance-only estimate with both directions shown explicitly, try the fiber latency calculator.
What this estimate includes
The equipment list includes documented latency values for Arista, Cisco, Juniper and Fortinet components. Open an element’s information button to find its source and caveats. Manufacturer figures often represent a minimum under specific conditions.
These estimates are based on manufacturers’ specifications. Packet size, forwarding mode, transceivers and queuing can change the result. Check the source documentation for your configuration and validate important designs with measurements of the actual network.
Browse the device latency table or read more about methodology, sources and frequently asked questions.