TCP Throughput Calculator
See what limits a TCP connection: the window, or packet loss.
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TCP Throughput Calculator by TheCalcTools
How the TCP Throughput Calculator works
Enter the window size, round-trip time, segment size and packet loss rate.
Window-limited throughput is the window divided by the RTT.
The Mathis model estimates the throughput ceiling caused by packet loss.
The formula
Worked example
Using the default values shown in the calculator:
| TCP window (KB) | 64 |
|---|---|
| Round-trip time (ms) | 50 |
| MSS (bytes) | 1460 |
| Packet loss (%) | 0.01 |
- A 64 KB window over 50 ms allows 64 × 1,024 × 8 ÷ 0.05 = 10.49 Mbps.
- With 0.01% loss, the Mathis ceiling is 28.61 Mbps.
- The lower of the two is the likely limit: Window.
Result:
| Window-limited throughput (Mbps) | 10.49 |
|---|---|
| Loss-limited throughput (Mbps) | 28.61 |
| Likely limit | Window |
Frequently asked questions
Is the Mathis formula exact?
No. It is a simple model for steady-state TCP Reno-like behaviour and gives an order-of-magnitude ceiling. Modern algorithms such as CUBIC and BBR behave differently.
How can I raise throughput on a long path?
Increase the window with window scaling, reduce loss, and consider a congestion-control algorithm designed for high BDP paths.
Sources and further reading
- Mathis et al., The Macroscopic Behavior of the TCP Congestion Avoidance Algorithm
- Wikipedia: TCP congestion control
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.