MB does not equal Mb

  • By Christopher Kielty, last updated September 07, 2016
  • Filed under: Networking

MB and Mb are not the same thing. In fact, they are quite different. How different? Eight times different. That’s right. One humble little megabyte equals a whopping eight megabits. Not so little.

A megabit is 1,000 bits. A megabyte is 1,000 bytes. While a bit can represent only two possible values (a 1 or a 0), a byte can represent 256 different values using its eight bits. Think of it this way: A bit is just an on/off value, but a byte can be a letter, number, symbol, 8-bit color value, etc. Bits and Bytes are quite different.

One megabyte equals eight megabits

Unfortunately, the only distinction between the two abbreviations is whether the, “B,” at the end is uppercase or lowercase. That can make it pretty difficult to notice which is which. This seems to be true both when reading and when writing.

The minute difference between the two abbreviations can make it pretty easy to overlook typos. Technically, MB and Mb are both are correct. It’s like one of those unfortunate situations where you mistype a word but the mistyped word is still a word. Much harder to catch, I think.

Perhaps an even more problematic situation would be when someone, for whatever reason, uses all caps. If they’re not careful, all of their bits will end up looking like bytes.

Think bytes when thinking disk size

Typically, megabytes are used to denote disk size. You might buy an SSD with a capacity of 240 GB. Ok, so that example didn’t actually use megabytes, but the same rules apply. One gigabyte is eight gigabits.

Think bits when thinking network speed

Bits, on the other hand, are typically used to indicate network speed. Gigabit ethernet, for example, is rated at one gigabit per second. So don’t expect that gigabit connection to transfer a gigabyte worth of data per second. A gigabit connection can handle 125 MB/s (1,000 / 8). Or can it? Well, no, it probably can’t. Because of various limiting factors, it probably isn’t reasonable to expect to see 125 MB/s when transferring files from one drive, over a network, to another drive. Still, that’s far better than 100BASE-T bandwidth (100 / 8). But I digress…

Alternative abbreviations for megabit and megabyte

Is there a better way? I suppose you could just write out megabit and megabyte. That’d do a pretty good job of avoiding all the confusion. However, if you must use an abbreviated form, I rather like Mbit and Mbyte.