Global Latency Calculator
Estimate round-trip latency from distance using the speed of light in fibre, plus per-hop and processing overhead.
Inputs
Real cable routes are typically 1.3–1.6× the great-circle distance.
About two thirds of the speed of light in vacuum.
Round-Trip Time
118.00ms
One-Way Propagation
56.00ms
Propagation Component of the RTT
112.00ms
Hop Overhead
6.00ms
Physical Floor in Vacuum
53.37ms
Distance Actually Travelled
11,200km
Cold Request Time to First Byte
369.00ms
Step by step
Values used
Great-circle distance = 8,000 km; Fibre path vs straight line = 1.40 ×; Signal speed in fibre = 200,000 km/s; Router hops on the path = 12 hops; Queueing and forwarding per hop = 0.2500 ms; Server processing time = 15 ms
Global Latency
RTT = 2 × great-circle distance × route factor ÷ signal speed in fibre, plus 2 × hops × per-hop delay; roughly 1 ms per 100 km in each direction.
Round-Trip Time
= 118.00 ms
One-Way Propagation
= 56.00 ms
Propagation Component of the RTT
= 112.00 ms
Hop Overhead
= 6.00 ms
Physical Floor in Vacuum
= 53.37 ms
Distance Actually Travelled
= 11,200 km
How it works
Propagation is pure physics: light in glass covers about 200 km per millisecond, so a 8,000 km link costs roughly 80 ms of round trip before anything else, and a realistic cable route adds another 40%. Hop and processing overheads are added on top, and a cold request pays roughly three round trips for DNS, TCP and TLS before the first byte arrives. No amount of server tuning beats the speed of light, so once the propagation floor exceeds your latency target the only fix is moving the endpoint closer — which is precisely the argument for an edge deployment.
Formula
Global Latency
RTT = 2 × great-circle distance × route factor ÷ signal speed in fibre, plus 2 × hops × per-hop delay; roughly 1 ms per 100 km in each direction.
- route factor
- How much longer the cable path is than the straight line
- signal speed
- About 200,000 km/s in fibre, two thirds of vacuum light speed
- per-hop delay
- Queueing and forwarding time added at each router, counted both ways
Frequently Asked Questions
How is Global Latency calculated?
RTT = 2 × great-circle distance × route factor ÷ signal speed in fibre, plus 2 × hops × per-hop delay; roughly 1 ms per 100 km in each direction. Propagation is pure physics: light in glass covers about 200 km per millisecond, so a 8,000 km link costs roughly 80 ms of round trip before anything else, and a realistic cable route adds another 40%. Hop and processing overheads are added on top, and a cold request pays roughly three round trips for DNS, TCP and TLS before the first byte arrives.
Why does Global Latency matter?
No amount of server tuning beats the speed of light, so once the propagation floor exceeds your latency target the only fix is moving the endpoint closer — which is precisely the argument for an edge deployment.
What values do I need to enter?
This calculator takes 6 inputs: Great-circle distance, Fibre path vs straight line, Signal speed in fibre, Router hops on the path, Queueing and forwarding per hop, Server processing time. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.