TCP Throughput Calculator
Shows why a fast link may still transfer slowly over distance.
Maximum throughput
— Mbit/s
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
What limits it —
Limit from the window — Mbit/s
Limit from packet loss — Mbit/s
Window that would fill the link —
The formula
window limit = window × 8 ÷ RTT loss limit ≈ (MSS × 8 ÷ RTT) × 1.22 ÷ √loss
The loss limit is the Mathis equation, an approximation for loss-based congestion control such as Reno that holds only at low loss, under about 1%. Modern algorithms can do better, and the sum does not cover protocol headers.
What to watch out for
TCP can only have one window of data unacknowledged at a time, so a longer round trip means a lower rate. Measure the round-trip time with ping.
Frequently Asked Questions
What limits a 64 KiB window at 50 ms?
10.5 Mbit/s, however fast the link is.
What does 0.01% loss do at 50 ms?
With a 1,460-byte segment, the Mathis estimate caps throughput at about 28.6 Mbit/s.