Mbps to MB/s

Internet speed tests report download speed in megabits per second, while a file transfer progress bar or a download manager reports in megabytes per second, and the two are separated by a factor of 8, since there are 8 bits in a byte. A connection advertised at 100 Mbps tops out at about 12.5 MB/s, not 100 MB/s, the single most common source of confusion about why a download feels slower than the advertised plan speed.

Estimating download time for a large game or software update runs the same conversion in reverse: a 50 GB game update showing an estimated download time assumes a transfer rate in MB/s, so a user whose ISP plan is sold as "300 Mbps" needs to convert that to roughly 37.5 MB/s first before the download manager's time estimate makes any sense.

One byte is defined as eight bits, so the conversion factor between a bit-based rate and a byte-based rate is always exactly 0.125, or its inverse, 8.

MB/s = Mbps × 0.125

A basic 25 Mbps broadband plan converts to 25 × 0.125 = 3.125 MB/s of real transfer capacity. A common 100 Mbps plan converts to 100 × 0.125 = 12.5 MB/s. A gigabit connection advertised at 1,000 Mbps converts to 1,000 × 0.125 = 125 MB/s.

Going the other way, multiply megabytes per second by 8: a download manager reporting 15 MB/s is pulling data at 15 × 8 = 120 Mbps.

Unlike many conversions, this one is exact with no rounding needed at all, since 8 bits per byte is a fixed definition, not a measured constant; any imprecision in a real download comes from network overhead and congestion, not from the conversion itself.

The mistake specific to this pair is reading "Mb" as "MB" or vice versa: a lowercase b means bits and an uppercase B means bytes, and mixing them up makes a connection look exactly 8 times faster or slower than it really is, a very easy typo to make when skimming a plan brochure or a speed test result.