Alongside price, speed is one of the key factors people talk about when it comes to choosing broadband. Broadband speed is measured in Megabits per second, commonly written as Mb or Mbps (as in 24Mb or 24Mbps). It essentially means the rate at which data is transferred either from (download) or to (upload) a website. Note that a Megabyte (the unit that most file sizes are measured in), for the reasons described below, is different from a Megabit, and unlike Megabits a Megabyte is commonly written in capital notation (i.e. MB or MBps).

The fundamental unit of digital data is the byte. All digital data is constructed from numerous bytes (much like the fundamental building block of a house may be a brick, but 1000′s of bricks are required to build a house). There are 8 bits in a byte, and as such, 1 Megabit per second (the unit internet speeds are measured in) is 8 times slower than 1 Megabyte per second!

It is therefore important to bare this difference in mind when working out how long a file of a size measured in Megabytes will take to download over an internet connection with a speed measured in Megabits per second.

To put this difference between bits and bytes into context, some key unit terms are defined by their number of bits and bytes in the table below:

Terminology	Number of bits	Number of bytes
Kilo-bit	~1000	~125
Kilo-byte	~8,000	~1,000
Mega-bit	~1,000,000	~125,000
Mega-byte	~8,000,000	~1,000,000
Giga-bit	~1,000,000,000	~125,000,000
Giga-byte	~8,000,000,000	~1,000,000,000

To put all of the above into the context of how long it would take to download some common file types on a 2 Megabits per second internet connection – if the maximum available speed was applied consistently throughout the download (in reality, for a variety of reasons, your internet speed will vary) then you could expect the files listed below to be downloaded within the following time frames:

File Type	Time Taken
Word document (around 50 Kilobytes in size)	~1/5th of a second
Average website, photo or music track (around 2.5 Megabytes in size)	~10 Seconds
Video (around 3 Gigabytes in size)	~3 hours, 20 minutes

In terms of data consumption:

 

• Streaming 60 minutes of standard definition video over the internet can consume between 50 and 255 Megabytes

Streaming 60 minutes of radio over the internet can consume over 60 Megabytes