Signal Propagation Delay Calculator
Enter the link distance and transmission medium to find one-way and round-trip propagation delay. Useful for network planning, PCB timing, fiber optic design and understanding latency in distributed systems.
m
Transmission medium
Time for a signal to travel the full distance once
- 1
Signal velocity in medium
299,792,458 m/s × 0.68 = 203,858,871 m/sSpeed of light in vacuum × velocity factor for this medium. - 2
One-way propagation delay (ns)
1,000 m ÷ 203,858,871 m/s × 10⁹ = 4,905.4
How does this calculator work?
Propagation delay = Distance ÷ (c × Velocity Factor). A 1000 m single-mode fiber link (velocity factor 0.68) gives a one-way delay of about 4.9 µs and round-trip of 9.8 µs. Coaxial cable (0.66c) and twisted pair (0.59c) are slightly slower. Vacuum / free space is fastest at the full speed of light.
Formula
How this is calculated
Signals in electrical and optical cables travel at a fraction of the speed of light in vacuum (c = 299,792,458 m/s). That fraction is called the velocity factor and depends on the dielectric material surrounding the conductor. Dividing the cable length by the signal velocity gives the one-way propagation delay; doubling it gives the round-trip delay relevant to protocols that wait for an acknowledgement.
Velocity factors used here: vacuum / free space = 1.00 (exact); single-mode optical fiber ≈ 0.68 (refractive index n ≈ 1.47); RG-58 coaxial cable ≈ 0.66; Cat5e/6 twisted-pair UTP ≈ 0.59. These are typical published values — exact figures vary by manufacturer and should be taken from the cable data sheet for precise timing analysis.
Note that propagation delay is only one component of total network latency. Processing delay in switches and routers, queuing delay under load, and serialisation delay (the time to clock out each bit) are additional contributors. This calculator isolates the pure speed-of-light component, which sets the irreducible minimum latency for any link.
Frequently asked questions
Glass has a refractive index of about 1.47, which slows light to roughly 68% of its vacuum speed — around 204,000 km/s. Over a 1000 km fiber link that still gives a one-way delay of nearly 5 ms. For intercontinental links of 10,000 km the one-way delay reaches about 49 ms regardless of bandwidth.
Propagation delay is purely the speed-of-light travel time across the physical medium. Total network latency also includes serialisation delay (time to transmit all bits at the line rate), processing delay in routers and switches, and queuing delay when buffers are shared. Propagation delay is the irreducible floor.
Protocols that require acknowledgements (TCP, HDLC) stall if the round-trip delay is long relative to the transmission window. This is the bandwidth-delay product problem. Long-haul links need large TCP window sizes, satellite links (≈600 ms RTT) require special tuning, and real-time applications like VoIP set a hard limit around 150 ms one-way delay for acceptable quality.
Also known as
TG we-Calculate Editorial Team. (2026). Signal Propagation Delay Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/propagation-delay-calculator
TG we-Calculate Editorial Team. "Signal Propagation Delay Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/propagation-delay-calculator.
TG we-Calculate Editorial Team, "Signal Propagation Delay Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/propagation-delay-calculator
@misc{wecalculate_propagation_delay_calculator, title = {Signal Propagation Delay Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/propagation-delay-calculator}}, year = {2026}, note = {TG we-Calculate} }
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