NetCalc
Dark mode
NC

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 calculates max theoretical throughput using 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 lets you extend that cramped 16-bit window field with a shift factor. The payoff: windows that climb all the way to 1 GiB. Skip it, and a single TCP flow chokes on fast long-distance links—you're leaving bandwidth on the table.

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

To saturate a 1 Gbps link at 100 ms RTT, you need a window of about 12.5 MB. Here's the math: BDP = 125 MB / s × 0.1 s ≈ 12.5 MB.