RTT Calculator
Calculate round-trip time between two network endpoints.
Inputs
Fiber ~0.67c, copper ~0.77c, wireless ~1.0c
Round-Trip Time
73.786ms
One-Way Delay
36.893ms
One-Way Propagation Delay
24.893ms
Total Processing Delay (one-way)
12.00ms
Step by step
Propagation speed
0.67 * 299792 km/s
= 200860.9 km/s
One-way propagation delay
5000 / 200860.9 * 1000
= 24.893 ms
Total processing delay
1 ms * 12 hops
= 12 ms
RTT
(24.893 + 12) * 2
= 73.786 ms
How it works
Round-trip time is twice the one-way delay, which itself is the sum of propagation delay (distance divided by signal speed in the medium) and processing delay at each hop along the path. Fiber optic signals travel at roughly 2/3 the speed of light due to the glass refractive index.
Formula
RTT
RTT = 2 * (distance / (c * speed_fraction) + processing_per_hop * hops)
- d
- Distance in km
- c
- Speed of light (299,792 km/s)
- f
- Propagation speed fraction
- p
- Processing delay per hop
- n
- Number of hops
Frequently Asked Questions
Why is fiber propagation speed only ~67% of light speed?
Light travels slower in glass (refractive index ~1.47) than in vacuum. The effective group velocity in standard single-mode fiber is approximately 200,000 km/s, or about 2/3 of the vacuum speed of light.
What contributes to processing delay at each hop?
Routers and switches need time to look up the destination in their forwarding table, check ACLs/QoS policies, and move the packet between input and output buffers. Modern routers typically add 0.1-5ms per hop depending on load and complexity.