Global Latency Calculator
Estimate round-trip latency from distance using the speed of light in fibre, plus per-hop and processing overhead.
About Global Latency Calculator
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
Worked example
With the default values below, Global Latency Calculator returns Round-Trip Time of 118.00. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Great-circle distanceaccepts 0–20,100 km
- 8,000 km
- Fibre path vs straight lineaccepts 1–3 ×
- 1.4 ×
- Signal speed in fibreaccepts 1,000–300,000 km/s
- 200,000 km/s
- Router hops on the pathaccepts 0–64 hops
- 12 hops
- Queueing and forwarding per hopaccepts 0–50 ms
- 0.25 ms
- Server processing timeaccepts 0–60,000 ms
- 15 ms
Results
- 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
- Cold Request Time to First Byte
- 369.00 ms
Step by step
- 1Values used
- 2Global Latency
- 3Round-Trip Time= 118.00 ms
- 4One-Way Propagation= 56.00 ms
- 5Propagation Component of the RTT= 112.00 ms
- 6Hop Overhead= 6.00 ms
- 7Physical Floor in Vacuum= 53.37 ms
- 8Distance Actually Travelled= 11,200 km
Assumptions and limits
- The result is derived only from the 6 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
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.