Calculate maximum theoretical TCP throughput using the bandwidth-delay product formula.
BDP = bandwidth × round-trip time. It is the minimum amount of data 'in flight' needed to keep a link saturated. If the TCP window is smaller than BDP, throughput is capped.
TCP waits for ACKs every RTT. A small window means few unacknowledged segments at once, so a long RTT leaves the link idle. Window scaling fixes this on 'long fat networks'.
RFC 1323 window scaling extends the 16-bit window field by a shift factor, allowing windows up to 1 GiB. Without it, a single TCP flow cannot fully use a fast long-distance link.
BDP = 125 MB / s × 0.1 s ≈ 12.5 MB. You need a window of about 12.5 MB to saturate a 1 Gbps link at 100 ms RTT.
Enter your bandwidth (in Mbps or Gbps), round-trip latency (in ms), and TCP window size. The calculator computes maximum theoretical TCP throughput using the formula: Throughput = Window Size / RTT. Adjust the window size to see how buffer tuning affects real-world performance, especially on high-latency links like satellite or transcontinental connections.
For typical broadband (100 Mbps, 20ms RTT, 64KB window), expected throughput is about 25 Mbps. Increasing the window to 1MB raises throughput to ~400 Mbps. For bandwidth unit conversions, try our Bandwidth Calculator. For network design calculations, use the IP Range Calculator.