Convert megabits to megabytes

The formula

megabytes = megabits × 0.125

megabits to megabytes — quick reference

A lowercase b is what makes 100 Mb/s feel like 12 MB/s

The advertised figure is megabits per second; the download panel counts megabytes. Eight bits to a byte, so a 100 Mb/s line resolves to 12.5 MB/s at its absolute ceiling. The number was never dishonest — the units changed halfway through the sentence, and one character, lowercase b against uppercase B, is all that marks the eightfold difference.

Then take a further slice off. TCP and IP headers, retransmits and the encryption on nearly everything now all ride inside that same line rate, so eight to ten per cent typically never reaches the file. A 100 Mb/s connection settling around 11.2 MB/s in a browser is behaving normally; one that never exceeds 3 MB/s has a genuine fault, and separating the two starts here.

This conversion is decimal, and the download panel may not be

A megabyte is treated here as 1,000,000 bytes, matching how network rates have always been quoted. Some download managers, and Windows itself, measure in binary units of 1,048,576 bytes while still printing "MB", which shaves a further 4.9% off the displayed speed. Two tools watching the same transfer can therefore disagree by roughly a twentieth.

Before blaming the line, check what is actually being measured. A single HTTP download rarely saturates a fast connection on its own, and Wi-Fi on a congested 2.4 GHz channel caps out well below what the cable delivers. Speed tests report megabits because that is what the contract promises; file transfers report megabytes because that is what a file is.

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