Network Latency Calculator

Light travels slower inside glass fiber than in a vacuum because of the fiber's refractive index, and 0.67 (about two-thirds of c) is the standard approximation used for typical single-mode fiber. The calculator multiplies the vacuum speed of light by this factor before dividing distance by it, which is why even a theoretically instant network still carries a fixed physical delay per kilometer of fiber.

Every hop that forwards the packet has to receive and re-transmit the full packet onto its outgoing link before passing it along, so the calculator adds one transmission delay per hop rather than treating it as a one-time cost at the source. This assumes every hop is at the same link speed and packet size as your inputs, which real mixed-speed paths won't always match exactly.

The calculator uses the Mathis formula, throughput ≈ MSS / (RTT × √loss), where RTT sits in the denominator directly and loss enters as a square root — so doubling RTT halves the throughput estimate, while quadrupling the loss rate only cuts throughput in half (since √4 = 2). This captures why long, lossy paths punish TCP performance far more than short, clean ones.

One-way latency sums propagation, processing, queuing, and transmission delay for a single direction of travel, and the calculator doubles that total to get round-trip time, implicitly assuming the return path is identical in distance, hop count, and congestion. Real networks often route asymmetrically, so an RTT you measure with a ping may differ from this doubled estimate even when your inputs are accurate.