Megabits and megabytes: why speeds differ by eight times

If the speed your Internet provider promised, the speed a speed test measures, and the speed NetWorx or NetGenius shows are far apart, you may be comparing bits (b) with bytes (B):

• megabits (Mb), or megabits per second (Mbps, Mb/s), with a lowercase ‘b’;
• megabytes (MB), or megabytes per second (MBps, MB/s), with an uppercase ‘B’.

Bits and bytes

One byte is eight bits. Anything measured in bits, kilobits, megabits or gigabits is therefore a number about 8 times larger than the same thing measured in bytes, kilobytes, megabytes or gigabytes.

Internet providers usually advertise the larger number. If one provider offered 10 MB/s and another 80 Mb/s, the second may look much faster, but the two speeds are the same. Always check whether the ‘b’ is lowercase or uppercase.

You can choose which unit our programs show:

• in NetWorx, choose a bits or bytes option for Speed on the Main page of Settings;
• in NetGenius, choose Bytes or Bits under Display format in Preferences.

Decimal and binary units

To add to the confusion, two systems are in use. In the decimal system kilo means 1000, while in the binary system it means 1024. Usually a lowercase ‘k’ stands for the decimal kilo and an uppercase ‘K’ for the binary one; ‘M’ for mega, ‘G’ for giga and ‘T’ for tera are the same in both.

Binary units also have names of their own, such as KiB (kibibyte) for 1024 bytes and MiB (mebibyte) for 1024 KiB, but they are rarely used, and “kilobyte” may mean either 1000 or 1024 bytes. Either way, this difference is small next to the one between bits and bytes.

Most commonly:

• 1 kilobit (kb) = 1000 bits
• 1 kilobyte (KB) = 1024 bytes = 1024 × 8 bits
• 1 megabit (Mb) = 1000 kilobits = 1000 × 1000 bits
• 1 megabyte (MB) = 1024 kilobytes = 1024 × 1024 × 8 bits

So to download 1 MB in one second you need a connection of about 1 MB/s, or 8 Mb/s. In the same way, a kilobyte is about 8 times a kilobit, and a gigabyte about 8 times a gigabit.