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What does it mean? Think of a water pipe. We can think of its bandwidth being related to the pipe's size or capacity (which is related to its diameter). The bigger the pipe the more water it can transport per second. A bigger pipe can transport a gallon of water more quickly than a smaller pipe. Both pipes can transport the water but clearly a gallon of water through a drinking straw will take a lot longer than a big water pipe.

Bandwidth is the measure of how fast our 1s and 0s can be transmitted. In the internet world you may often hear people talk about pipes because it’s easy to relate to as I have explained above.

Still with me? Great, you’re doing well 😊

Let's Go Deeper

Internet service providers (ISP) usually talk about bandwidth in terms of Mb/s – mega-bits per second. And we all know how much they boast about offering extreme high speed but that often it can be … very … very … (yawn) …. Slow!

Think of bandwidth as flow rate of water which is measured in litres per second. So water poured through a drinking straw is probably going to take (I am guessing here!) about a minute to fill a one litre container. Water poured through a hosepipe might take (again, wild guess) five seconds to fill that same one litre container. And water through a pipe that is one metre in diameter ... well, that container is going to be filled in moments, maybe less than half a second.

Let’s go back to our simple message – we want to send the word “Bad” which is 24 bits.

Let’s say the ISP we use offers 200Mb/s (Mega-bits per second) –
200 x 1,024 x 1,024 = 209,715,200 bits per second.

Simplistically, this means to transmit “Bad” would take:

24 (3 characters of 8 bits each)  / 209,715,200 seconds = 0.00000011444091796875 seconds or 0.11444091796875 microseconds.

That’s a ridiculously tiny, microscopic amount of time.

Now, when you take a stunning photo with your hi-res smartphone camera, you could easily end up with a photo file that is 3.5MBytes. Think of the filesize as your water container. As you have remembered 3.5MBytes is

3.5 x 8 Mbits or 3.5 x 1024 x 1024 x 8 = 29,360,128 bits.

So repeating the above exercise we get

29,360,128 / 209,715,200 = 0.14 seconds – wow! Quite a difference.

Now as you will see in another module, when you create a web page it is important to be aware of the images and photos because they make up a large amount of data.

Real-World use cases:

Load a web page with 8 photos like the one above and you are looking at 8 x 0.14 = 1.12 seconds to load the web page into your browser. Add in the following variables:

  • data added for transmission
  • the journey time of the photos from the server they are stored to the browser where viewed
  • inconsistent bandwidth across the internet connection
  • possibly viewer’s mobile phone 3G connection
  • error correction and data traffic collisions
  • all the other web page elements (HTML, JavaScript, cascading style sheets, fonts)

And suddenly the user’s experience could be that it takes many seconds for their browser to load your web page.

With the internet, everyone will be connected in different ways, through different ISPs and technologies. Developing countries may not have fibre optic and indeed you may find that many countries have users with only mobile phone 3G connectivity.

End to end speed is restricted by the weakest link. Just because your ISP’s servers can communicate with your laptop at 200Mb/s does not mean that everything you do will be delivered at that speed. If you view a website hosted in a developing country that only has infrastructure capable of 10Mb/s then you can be sure that is going to create a slower web browsing experience.

There are two variables - the amount data transmitted and the speed at which it is transmitted. So keep the former as small as possible (i.e. small file size) and the latter as high as possible (your ISP's bandwidth) although you have less control over this.


  • A byte = 8 bits
  • Bandwidth (flow of water) is usually expressed in Mbit/s – so 1 Mbit/s = 1,024 x 1,024 bits / second = 1,048,576 bits per second.
  • Computer file sizes (water container size) such as photos (jpg), images (png) are expressed in kilo-Bytes - kBytes (kB), Mega-Bytes (MB).
  • bandwidth -> flow rate
  • filesize -> container size

The confusion can be in the units because b is used for bit and B is used for Byte.

So, 3 kB means 3 kilo-Bytes whereas 3 kb means 3 kilo-bits, a factor of 8 smaller. And remembering that not everywhere you read will use the strictly correct units will make it more confusing!

The higher the bandwidth the quicker data can be transmitted.

Be sure you recognise the notation - Mb is mega-bit whereas MB is mega-byte. It is easy to see why this can be confusing - the capitalisation of the 'B' makes it 8 times bigger. so Mbps is megabit per second, MBps is megabyte per second. Strictly speaking, Mbps is the more correct term to use when expressing bandwidth. However, file sizes will always be expressed in kBytes (kB) or Mbytes (MB). Also note the capitalisation of the M for mega to distinguish from milli, m. The joy of the decimal number system 🙂

At least you now have an insight into what bytes are all about, and why it is important to have some idea of what it means. Also to understand file sizes and how data gets sent across the internet and what bandwidth means and why it is important.

  • 👍 TIP – Make sure you're keeping a watchful eye on the notation, so as not to get confused about the file size.

Recommended Resources

  • Free Tools

M-Lab's Speed Test provides advanced diagnostics of the performance of your broadband connection through quick measurements. 

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