Network Engineering
TCP Window Size Calculator
Enter link bandwidth and round-trip time to compute the bandwidth-delay product, optimal TCP window size, and maximum achievable throughput.
Calculations run locally in your browserTool
Example — Representative default scenario — bandwidth mbps 100 · rtt ms 50.
Bandwidth-delay product
625,000 bytes
optimal window size
Max throughput (default window)
10.5 Mbps
65KB window at 50ms RTT
Window scaling needed
Yes — enable TCP window scaling
Recommended window
610KB
to fully utilize 100Mbps
About this tool
TCP Window Size Calculator
The TCP Window Size Calculator computes bandwidth-delay product, optimal receive window, and maximum throughput from link bandwidth and RTT, with Linux buffer tuning parameters.
• Calculate required TCP buffer size for a high-bandwidth cross-region link
• Understand why a 1Gbps link between distant datacenters achieves only 100Mbps throughput
• Compute bandwidth-delay product before tuning Linux TCP buffer parameters
• Model throughput impact of increasing RTT in a cloud region migration
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FAQ
What does this tool tell you?
The TCP Window Size Calculator computes bandwidth-delay product, optimal receive window, and maximum throughput from link bandwidth and RTT, with Linux buffer tuning parameters.
What affects the result most?
TCP window size limits throughput: max_throughput = window_size / RTT. Window scaling: TCP window scale option extends max window from 65KB to 1GB. Bandwidth-delay product: optimal window size = bandwidth × RTT — fill the pipe.
How should I use the result?
The calculation is deterministic — the same inputs always produce the same output — so the most useful workflow is to vary one input at a time and see which factor moves the result most. That tells you where to focus your attention before committing to a decision.
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