Glossary · Networking

Throughput

Throughput is the amount of data actually delivered across a network per second, which is usually lower than the link's rated bandwidth.

Updated October 6, 2026

Throughput is the measured rate of successful data transfer between two points. It is affected by bandwidth, latency, packet loss, protocol overhead and the speed of the endpoints.

Why it matters

Throughput is what users and applications actually experience. TCP throughput on a single connection is limited by window size and round-trip time, so a distant server can deliver much less than a nearby one on the same link. Monitoring throughput over time reveals congestion that a nominal bandwidth figure hides.

When comparing tests, note the direction (upload or download), the number of parallel connections and the distance to the test server.

Example

$ iperf3 -c server.example.net
[ ID] Interval        Transfer    Bitrate
[  5] 0.00-10.00 sec  1.05 GBytes  900 Mbits/sec

On a 1 Gbps link, 900 Mbps of measured throughput is typical because of headers, acknowledgements and other overhead.

Common mistakes

  • Quoting the plan's bandwidth as your expected throughput.
  • Testing against a single distant server and blaming the local connection.
  • Ignoring Wi-Fi, which often caps throughput below the wired link.

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