RTT Calculator
Calculate round-trip time between two network endpoints.
About RTT Calculator
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
Worked example
With the default values below, RTT Calculator returns Round-Trip Time of 73.786. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Distanceminimum 0 km
- 5,000 km
- Propagation Speed (fraction of c)accepts 0.01–1
- 0.67
- Processing Delay (per hop)minimum 0 ms
- 1 ms
- Number of Hopsminimum 1
- 12
Results
- Round-Trip Time
- 73.786 ms
- One-Way Delay
- 36.893 ms
- One-Way Propagation Delay
- 24.893 ms
- Total Processing Delay (one-way)
- 12.00 ms
Step by step
- 1Propagation speed= 200860.9 km/s
- 2One-way propagation delay= 24.893 ms
- 3Total processing delay= 12 ms
- 4RTT= 73.786 ms
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
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.