How to convert from Mbps to MB/s

One of the first tools I developed was for converting bitrates: the toolstud.io bandwidth converter. I was frustrated with having to translate ADSL bitrates (in Mbps) into the time needed to download a file of e.g. 10MB. I wanted to convert those Mbps into MB/s numbers, with Mbps = megabit per second and MB/s = megabyte per second.

Conversion didn’t seem too hard. A byte is 8 bits, therefore 100 megabits = 100/8 megabytes. So 100 Mbps (which was the speed of standard Ethernet networks when I developed the tool) = 12.5 MB/s, which translates to 750 MB/min, etc.

This means that -in theory- a full 💿 CD (+- 750 MB) could be transferred over a 100Mbps network connection in +- 1 minute. In practice, it would be dependent on hardware quality and the other traffic on the same connection what top speed could be reached. But always less than 750MB/min.

Another example: say that you mobile operator gives you a data limit of 10 GB/month. Is this enough to continuously stream Spotify music over it for 12 hours a day? Let’s do the calculation.

This translates to 30.9Kbps. So if you did 24/7 streaming, you can only use 30.9 Kbps in order not to go over the 10GB/mon limit. Spotify, however, needs at least 96 kbps. This translates into 31.1 GB/month. Even if you would only stream 50% of the time, you would still need 16GB/month to cover this.

I originally was confused by some people’s usage of megabyte as 1024 * 1024 bytes instead of 1000 * 1000 bytes. This confusion was solved in 1998 when the International Electrotechnical Commission (IEC) decided that ‘mega’ would always mean 1000 * 1000. For binary units, the terms kibibyte/mibibyte/gibibyte/… were proposed. Unfortunately this is not what operating systems use.

You might have noticed that after formatting a 500GB hard disk, you only see a volume of e.g. 465 GB. What they mean is: 465 GiB or gibibyte. 465 * 1024 * 1024 * 1024. In the calculator I always use this distinction between the decimal system (megabyte) and the binary system (mibibyte).

Decimal vs binary units

• megabyte = 1000 * 1000 bytes
• mibibyte = 1024 * 1024 bytes