Work out round trip time estimate instantly with clear inputs, formula shown and shareable results.
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.
RTT estimate
propagation = distance / propagation speed; one-way = propagation + hops x per-hop delay; RTT = 2 x one-way
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.
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.