Calculator Inputs
Use total path distance per direction. The tool multiplies only per-hop delays by hop count.
Plotly Graphs
Latency Component Breakdown
This graph separates propagation, transmission, processing, and queue contributions for both directions.
Packet Size Sensitivity
This curve shows how forward one-way latency changes as payload size grows under the current assumptions.
Example Data Table
| Scenario | Payload (bytes) | Bandwidth (Mbps) | Distance (km) | Hops | Estimated Base One-Way (ms) | Estimated Worst One-Way (ms) |
|---|---|---|---|---|---|---|
| LAN voice | 160 | 1000 | 2 | 3 | 0.4652 | 0.6652 |
| Metro video | 1200 | 100 | 35 | 5 | 2.6774 | 3.3774 |
| WAN interactive | 1400 | 50 | 250 | 8 | 11.1109 | 12.6109 |
| IoT uplink | 300 | 10 | 15 | 4 | 3.9691 | 4.8691 |
Formula Used
Total Packet Bytes = Payload Bytes + Protocol Overhead Bytes
Propagation Delay = Distance / (Speed of Light × Velocity Factor)
Transmission Delay Per Hop = Packet Bits / Link Bandwidth
One-Way Base = Propagation + (Transmission Per Hop × Hops) + (Processing Per Hop × Hops) + (Queue Per Hop × Hops)
RTT = Forward One-Way Base + Return Control One-Way Base
Transaction Latency = (Handshake RTTs × RTT) + Forward One-Way Base + Optional Return Control One-Way Base
Maximum Payload ≈ ((Target Budget − Fixed Delays) × Bandwidth ÷ Hops) − Protocol Overhead
Fixed delays include propagation, processing, queue delay, and jitter allowance. This model estimates steady-state behavior and does not include retransmissions, congestion collapse, routing changes, or application think time.
How to Use This Calculator
- Enter your payload size and protocol overhead in bytes.
- Set forward and return bandwidth for asymmetric links if needed.
- Enter the total path distance for each direction.
- Choose realistic velocity factors for fiber, copper, radio, or mixed media.
- Set the hop count and per-hop processing and queue estimates.
- Add jitter and any handshake round trips required before data transfer.
- Specify a one-way latency target to test design feasibility.
- Press Calculate Latency to show results above the form.
- Review the graphs, result table, and budget margin.
- Use the CSV or PDF buttons to save the calculated output.
Frequently Asked Questions
1) What is the difference between one-way latency and RTT?
One-way latency measures delay from sender to receiver. RTT measures the forward trip plus the return trip. RTT matters for acknowledgments, handshakes, and request-response applications.
2) Why does hop count increase latency?
Each hop usually adds serialization, processing, and queue time. Even when distance stays constant, more devices in the path often increase end-to-end delay.
3) Should distance be per hop or total path distance?
Enter total distance for the selected direction. The calculator multiplies only per-hop processing, queue, and serialization effects by the hop count.
4) What does velocity factor mean?
Velocity factor represents how fast a signal travels through a medium compared with the speed of light in vacuum. Fiber often uses values near 0.67.
5) Why do larger packets increase delay?
Larger packets take longer to serialize onto a link. That transmission delay appears at each hop, so packet size can materially affect total latency on lower-bandwidth paths.
6) Should I use average queue delay or peak queue delay?
Use average values for normal planning and use higher estimates when designing for service guarantees or real-time worst-case performance.
7) Does this include packet loss or retransmissions?
No. The model estimates deterministic and budgeted delay components. Loss, retransmissions, congestion events, and routing changes can increase real observed latency.
8) When would I disable the return ACK option?
Disable it when you only want forward-path latency or when modeling one-way media flows where acknowledgment timing is not part of the target measure.