A speed test transfers data between your device and a remote server and divides transferred bits by elapsed time. Results are influenced by server location, test duration, protocol overhead, browser limits, Wi-Fi conditions and other traffic.
Why larger tests help
Very small transfers may finish before a connection reaches representative throughput. Adaptive tests use more data on faster links.
Why results differ
Different services use different servers, parallel connections, algorithms and measurement windows.
Data usage
Full diagnostics consume more data than quick checks. Use quick checks on limited cellular plans when you only need a basic health indication.