Network Latency Budget Calculator

Frequently Asked Questions

What makes up network latency?

Propagation (distance ÷ signal speed - ~5 µs/km in fiber), serialization (packet bits ÷ link rate), plus per-hop processing and queuing delay. Round-trip is roughly twice the one-way sum.

Why can't latency beat the speed of light?

Propagation is bounded by physics: ~5 µs per km in fiber (~⅔ c). New York–London is ~28 ms one-way minimum no matter the bandwidth.

Does more bandwidth reduce latency?

Only the serialization component. Once links are fast, propagation and queuing dominate - which is why adding bandwidth often doesn't fix lag.

What is a typical latency budget?

Interactive voice/video target < 150 ms one-way; gaming wants < 50 ms RTT. The tool shows where the budget is spent so you can target the biggest term.

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Estimates for informational purposes only.

Important Disclaimer: Estimates for informational purposes only.

This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How This Calculator Works

End-to-end latency is the sum of three independent delays. Propagation is distance ÷ signal speed: light in fiber travels about 200 km/ms (~5 µs/km), copper ~182 km/ms, and free-space radio near c at ~300 km/ms. Processing/queuing is the per-hop delay each router adds, multiplied by the hop count. Serialization is the time to clock the packet onto the wire: (packet bits) ÷ (link bits per second), incurred at each hop. One-way latency is the sum of all three; round-trip time (RTT) is roughly twice that, which is what ping and TCP handshakes actually feel.

Worked Example

1,000 km over fiber, 8 hops at 0.5 ms each, 1,500-byte packets on 1,000 Mbps links. Propagation = 1000 ÷ 200 = 5.0 ms. Processing = 8 × 0.5 = 4.0 ms. Serialization per hop = (1500 × 8) ÷ 1,000,000,000 × 1000 ≈ 0.012 ms, × 8 hops ≈ 0.096 ms. One-way ≈ 9.1 ms, RTT ≈ 18.2 ms. Note that distance dominates here - serialization on fast links is almost negligible, which is why physics, not bandwidth, sets the floor on long-haul latency.

Real-World Use

Architects use a latency budget to decide where to place servers, CDNs, and database replicas. Trading systems shave microseconds by shortening fiber routes; game and VoIP designers target sub-150 ms RTT; storage replication has hard distance limits because synchronous writes pay RTT on every commit. This breakdown shows whether a slow path is a physics problem (move closer) or a congestion problem (add capacity/reduce hops).

Common Mistakes

Assuming the speed of light in a vacuum: fiber is only ~67% of c, so use ~200 km/ms, not 300.

Ignoring the return trip: applications wait on RTT, not one-way delay - always double it for request/response.

Confusing bandwidth with latency: a 10× faster link barely changes serialization once packets are small relative to link speed.

Forgetting queuing under load: per-hop delay balloons when links are congested - this tool models nominal, not saturated, conditions.

Limitations & Related Tools

This is a planning estimate using nominal per-hop delays; real queuing latency is load-dependent and bursty, and routing paths can be longer than great-circle distance. It does not model jitter, TCP slow-start, or application processing time. Pair it with a bandwidth/throughput calculator for transfer-time estimates and with the Subnet planner when designing the underlying topology. Measure with ping/traceroute to validate assumptions against the live path.

Network Latency Budget Calculator

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