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TCP Throughput Calculator

Calculate maximum theoretical TCP throughput using the bandwidth-delay product formula.

0 Mbps / 1000 Mbps

How to use the tcp throughput calculator

  1. Enter the TCP window size in KB and the round-trip time in ms.
  2. The tool computes maximum theoretical throughput via the bandwidth-delay product.
  3. Compare against your link rate to see whether window scaling is needed.

Frequently asked questions

What is the bandwidth-delay product (BDP)?

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.

Why does high RTT cap TCP throughput on big links?

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'.

How does TCP window scaling help 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.

What window size do I need for 1 Gbps at 100 ms RTT?

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.