Round Trip Time Estimate Calculator

Work out round trip time estimate instantly with clear inputs, formula shown and shareable results.

About Round Trip Time Estimate Calculator

Light travels through fibre at about two-thirds of its vacuum speed, roughly 200,000 km per second, which gives 5 microseconds per kilometre one way or 10 microseconds round trip. That physics floor cannot be optimised away, so a London to Sydney round trip is at least 170 ms. Router processing and queueing add on top, and a geostationary satellite hop alone costs about 238 ms each way.

Formula

RTT estimate

propagation = distance / propagation speed; one-way = propagation + hops x per-hop delay; RTT = 2 x one-way

Worked example

With the default values below, Round Trip Time Estimate Calculator returns Estimated round-trip time of 69.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

One-way distanceminimum 0.1 km: 5,500 km
Transmission mediumone of Fibre optic (~200,000 km/s), Copper (~200,000 km/s), Free space / microwave (~300,000 km/s), Geostationary satellite hop: Fibre optic (~200,000 km/s)
Router hopsminimum 0: 14
Processing delay per hopminimum 0 ms: 0.5 ms

Results

Estimated round-trip time: 69.00 ms
One-way propagation delay: 27.50 ms
One-way hop processing delay: 7.00 ms
Physics floor for this distance: 55.00 ms

Step by step

1Values used
2RTT estimate
3Estimated round-trip time= 69.00 ms
4One-way propagation delay= 27.50 ms
5One-way hop processing delay= 7.00 ms
6Physics floor for this distance= 55.00 ms

Assumptions and limits

The result is derived only from the 4 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

Why is my measured RTT higher than the calculation?

Real fibre routes are not straight lines — actual path length is typically 1.3 to 2 times the great-circle distance — and queueing adds variable delay.

Can anything beat fibre latency?

Microwave and hollow-core fibre carry signals nearer to vacuum speed and are used on latency-critical financial routes, at much lower capacity and much higher cost.