TCP Transfer Time Estimator
Estimate ideal data time plus explicit round-trip startup latency.
Separate transfer time from startup latency
A simple transfer estimate starts with payload bits divided by sustained throughput, then adds startup delays measured in round trips. This calculator treats the entered size as decimal megabytes, the rate as decimal megabits per second, and adds RTT multiplied by the chosen handshake count. It reports data time, latency time, and their sum separately.
The defaults use 100 MB, 100 Mbps, 40 ms RTT, and two startup round trips. The payload takes 8.000 seconds at the entered sustained rate, the explicit startup cost is 0.080 seconds, and the estimated total is 8.080 seconds. Non-positive throughput and negative size or latency values are rejected.
An idealized estimate with explicit assumptions
This is not a TCP slow-start simulator. The throughput field should already represent a realistic sustained application rate after congestion, overhead, loss, and competing traffic. TLS, DNS, connection reuse, retransmission, and server response delays can add time beyond the selected round trips. Calculation stays in your browser. Compare the estimate with measured transfers and adjust assumptions rather than treating it as a benchmark.
Frequently Asked Questions
Why does a 100 MB transfer at 100 Mbps take eight seconds?
A byte contains eight bits, so 100 decimal megabytes equals 800 megabits before protocol overhead.
Does this model TCP slow start?
No. Enter a realistic sustained throughput and use startup round trips only for explicit connection latency.
What should handshake round trips include?
Include the connection, security, or request-response round trips that occur before useful transfer at your chosen measurement boundary.
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