How it works: The test downloads files of known size from public Content Delivery Networks and measures how long they take to arrive — that gives the download number in megabits per second. Latency is measured by sending small requests to several endpoints and taking the lowest round-trip time. Upload is estimated rather than directly measured, because measuring an upload requires a server we control to receive the bytes. 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, CDN availability, and the device you are testing on.