The three phases of a speed test
Most speed tests, including SpeedFast, run three measurement phases in sequence: latency (ping), download speed, and upload speed. Each phase tests a different aspect of your connection, and each requires a different measurement approach. Some tests also measure latency during the download and upload phases separately, which reveals bufferbloat — SpeedFast does this.
Why multiple connections matter
A single TCP connection almost never reaches your connection's full capacity — TCP's congestion control algorithm deliberately ramps up slowly and backs off when it detects any packet loss. This is good behavior for the internet's health, but it means a single-stream test understates what your connection can actually sustain.
That's why speed tests open several parallel connections and measure their combined throughput. This mirrors real-world usage, where your browser, streaming service, and background updates all use multiple connections simultaneously.
Handling the slow start
Every new TCP connection begins with a slow start — sending only a small amount of data initially and ramping up as it confirms packets are arriving safely. This means the first second of any measurement understates the sustained speed. Speed tests handle this by measuring for several seconds and discarding the initial ramp-up period before calculating the final result.
Server selection and distance
The server you test against affects the result significantly. A server across the ocean will show higher ping and often lower throughput than a nearby one — not because your connection is different, but because of the physical distance and number of network hops. SpeedFast runs on Cloudflare's global edge network, which routes your test to a nearby server automatically. For more detail on SpeedFast's specific approach, see our measurement methodology.
What the result actually represents
A speed test result is a snapshot, not a guarantee. It shows what your connection delivered during those specific seconds, against that specific server, with whatever else was happening on your network. Results will vary between tests for legitimate technical reasons. The most representative picture comes from running several tests at different times of day.
Run a speed test now and see how your connection performs against SpeedFast's edge network.