# Can propagation speed be measured in bits per second?

In networking, propagation speed is usually measured in meters per second. If we knew how many bits fit in a meter we could multiply these values and end up with a measurement in bits per second. Does such a unit make sense?

If we knew how many bits fit in a meter we could multiply these values and end up with a measurement in bits per second.

That's exactly the serialization rate - just do the math. While that rate is an important parameter it doesn't tell you anything about the propagation speed of any bit traveling the channel, ie. how long it takes for a transmitted bit to arrive at the other end.

• I'm not sure I understand your second sentence. The propagation speed alone, does not tell as anything about how long it takes for a transmitted bit to arrive at the other end, unless we also know the length of the physical medium. I would imagine that equivalently, if we knew how many bits we are tranferring and the serialization rate, we could divide the former by the latter and as such compute the propagation delay.
– Nick
Commented Oct 22, 2023 at 18:05
• No, you can't - the serialization rate is unrelated to the length of the medium, which you've canceled out by multiplying bit/m and m/s.
– Zac67
Commented Oct 22, 2023 at 18:39
• m/(m/s) = s. Similarly bits/(bits/s) = s.
– Nick
Commented Oct 22, 2023 at 18:47
• That s is the serialization delay since it relates to bit rate, not propagation rate.
– Zac67
Commented Oct 22, 2023 at 18:50
• I did not suggest it is propagation rate but propagation delay. Here's the math: We know that propagation delay is measures in m/(m/s) units and that 1m = n bits. Then m/(m/s) = n bits/(m/s • n bits/m) = n bits/(n bits/s) = s.
– Nick
Commented Oct 22, 2023 at 18:57