Throughput

What It Means

Throughput is the real-world measured speed of data successfully transferred across an internet connection, always lower than the theoretical bandwidth ceiling advertised by the ISP. A 100 Mbps nominal plan typically delivers 85 to 95 Mbps of measured throughput due to a stack of overheads: TCP/IP headers consume 3 to 5% of each packet, ethernet framing adds another 1 to 2%, encryption (TLS, QUIC) can reduce effective throughput 2 to 5%, Wi-Fi standards add variable 10 to 50% overhead depending on version and signal strength, and ISP DOCSIS or GPON scheduling adds 1 to 3%. Speed tests measure throughput, not bandwidth, Ookla Speedtest opens 4 to 16 parallel TCP streams to saturate the link, M-Lab NDT measures single-stream TCP throughput which better reflects real-world browsing, and Netflix Fast.com measures download throughput against Netflix CDN servers embedded in ISP networks. Factors that reduce throughput below expected levels include distance from the Wi-Fi router, outdated ethernet cables (Cat5 limits to 1 Gbps at short ranges), old modem firmware, MTU mismatch issues, and peak-hour congestion. The FCC Measuring Broadband America program publishes quarterly reports showing that most major ISPs deliver 95%+ of advertised speeds during normal hours, with cable operators dipping to 80 to 90% during 7 to 11 PM peak. If a speed test consistently shows less than 80% of plan speed on a wired ethernet connection, the Broadband Grade speed tool flags it as a potential ISP problem worth a support ticket.

Frequently Asked Questions