Propagation Delay Calculator & Simulation

Q: What is the propagation delay formula?

d_prop = (d)/(s), where d is the length of the physical link in metres and s is the propagation speed of the signal in metres per second — about 2 × 10^8 m/s in fibre and 3 × 10^8 m/s in free space.

About this simulator

Propagation delay is how long a signal takes to travel from one end of a link to the other. It depends on the length of the link and the speed of the signal in the medium, which is roughly two-thirds of the speed of light in cable. The simulation shows the first bit and the last bit of a packet moving along the link so you can see how it differs from transmission delay.

How it works

Signals move through copper or fibre at roughly two-thirds of the speed of light (about 2 × 10⁸ m/s).
The first bit needs $d / s$ seconds to reach the far end; every other bit follows the same journey.
A longer cable adds delay; a faster link does not make the signal travel faster.

Formulas used

$d_{\text{prop}} = \dfrac{d}{s}$
$d$ = link length (metres), $s$ = propagation speed (m/s)

Worked example

A 2,000 km optical-fibre link with a propagation speed of $2 \times 10^{8}$ m/s has $d_{\text{prop}} = \dfrac{2\,000\,000\ \text{m}}{200\,000\,000\ \text{m/s}} = 0.01\ \text{s} = 10\ \text{ms}$ . A geostationary satellite hop of 35,786 km at $3 \times 10^{8}$ m/s needs about $119\ \text{ms}$ each way — which is why satellite links feel slow even when the bandwidth is high.

Enter these numbers in the simulator above to see every step.

When to use it

Estimating round-trip time (RTT = 2 × propagation delay) for long links.
Explaining why upgrading bandwidth cannot remove latency caused by distance.
Solving numerical problems that combine transmission and propagation delay.

Frequently asked questions

What is the propagation delay formula?

$d_{\text{prop}} = \dfrac{d}{s}$ , where $d$ is the length of the physical link in metres and $s$ is the propagation speed of the signal in metres per second — about $2 \times 10^{8}$ m/s in fibre and $3 \times 10^{8}$ m/s in free space.

Does bandwidth change propagation delay?

No. Bandwidth changes how fast bits are sent (transmission delay). Propagation delay stays the same because the signal speed and the distance do not change.

Why is satellite internet slower to respond?

A geostationary satellite is about 35,786 km above the Earth, so each trip up and down adds over a hundred milliseconds of propagation delay, no matter how high the bandwidth is.