How it works: The test runs entirely in your browser against Cloudflare's global speed-test network, so it connects to a server close to you. It first measures
latency (ping) with a dozen tiny round trips and reports the median, plus
jitter — how much those round trips vary. It then measures
download by pulling data over several parallel connections for about eight seconds, and
upload by sending random data back the same way; the first second of each is ignored so connection ramp-up does not drag the result down. While the line is busy it keeps pinging, which reveals
latency under load. For a deeper explanation, see
Understanding Internet Speed,
what a latency test measures,
how latency relates to download and upload speed and
why speed test results vary. If your upload figure is far below your download,
here is what that means. If your result is lower than expected, work through
how to fix slow internet. Results depend on network conditions, Wi-Fi quality, and the device you are testing on. A full test transfers roughly 10–100 MB on a typical connection (more on gigabit lines) — keep that in mind on a metered mobile plan.