What is Bandwidth?

Bandwidth is the amount of data that a method of communication can transfer over a given time. In computer networks (e.g. the Internet), bandwidth is typically measured in megabits per second (Mbps).

What is a megabit per second? We'll define the terms below:

Mega (M)
In computer networking, we use SI metric prefixes to denote numbers of units. Mega (M) indicates one million units.

Bit (b)
A bit is the smallest unit of data in a computing system. It is commonly represented by a 0 or 1.

Megabit (Mb)
Given that mega (M) denotes one million units, and a bit (b) is the smallest unit of data, then a megabit (Mb) must be 1,000,000 bits. Another way to say this is a megabit can be thought of as one million 0s or 1s.

Megabits per Second (Mbps)
Putting it together, megabits per second is the number of millions of bits transferred during 1 second of time. For example, a 1 Mbps network connection can transfer 1,000,000 bits in a second. A 100 Mbps connection could transfer 100,000,000 bits in a second.

Megabits and Megabytes

While connection speeds are typically measured in bits, computer memory tends to be measured in bytes. This difference can be confusing if you're not familiar with these units and what they represent. A byte consists of eight bits. Therefore, measurements of computer memory (bytes) are eight times larger than measurements of connection speeds (bits).

Without the above understanding, it's easy to overestimate the speed of a connection. For example, if a user wishes to download a 10 MB (megabyte) file using a 1 Mbps (megabit per second) connection, they could incorrectly conclude that the download will take 10 seconds to complete.

10 MB / 1 Mbps = 10 Seconds

However, since we know that measurements of computer memory are eight times larger than measurements of connection speeds, we must first multiply the download size by 8 to convert it from megabytes to megabits. So, in terms of megabits, the file has a size of 80. Consequently, the actual download time will be closer to 80 seconds.

(10 MB * 8 bits per byte) / 1 Mbps = 80 Seconds

Network Protocol Overhead

In practice, it will actually take a little longer than 80 seconds for a 1 Mbps connection to download a 10 MB file. This is because some of the connection's usable speed is consumed by communication protocol overhead.

Click here to learn more about connection speeds and protocol overhead.