The calculation
A worked example
100 Mbps equals 12.5 MB/s, or approximately 11.92 MiB/s, before overhead and other limits.
The capital B matters
A bit is not a byte. Internet rates are generally advertised in megabits per second (Mbps), while file-transfer apps may show megabytes per second (MB/s). There are eight bits in a byte, so divide by eight before comparing a speed test with a file transfer.
Then check the prefix
A decimal megabyte contains 1,000,000 bytes. A mebibyte (MiB) contains 1,048,576 bytes. Some software labels a binary value “MB” even when it means MiB. That convention can introduce another difference beyond the factor of eight.
This is a unit conversion, not a prediction of usable throughput. Your application will generally see less than the nominal line rate because of protocol overhead, contention or a slower destination. Use the transfer-time calculator to model those planning assumptions explicitly.
Source & further reading
NIST: prefixes for binary multiples
Model reviewed October 25, 2026. Read our methodology and limitations.