What Is Bandwidth?

Everything you need to know about bandwidth and how to calculate what you need

A picture of water running from a faucet
© Glow Decor / Glow / Getty Images

The term bandwidth has a number of technical meanings but since the popularization of the internet, it has generally referred to the volume of information per unit of time that a transmission medium (like an internet connection) can handle.

An internet connection with a larger bandwidth can move a set amount of data (say, a video file) much faster than an internet connection with a lower bandwidth.

Bandwidth is typically expressed in bits per second, like 60 Mbps or 60 Mb/s to explain a data transfer rate of 60 million bits (megabits) every second.

How Much Bandwidth Do You Have? (& How Much Do You Need?)

See How to Test Your Internet Speed for help on how to accurately determine how much bandwidth you have available to you. Internet speed test sites are often, but not always, the best way to do that.

How much bandwidth you need depends on what you plan on doing with your internet connection. For the most part, more is better, constrained of course by your budget.

In general, if you plan on doing nothing but Facebook and the occasional video watching, a low-end high-speed plan is probably just fine.

If you have a few TVs that will be streaming Netflix, and more than a few computers and devices that might be doing who-knows-what, I'd go with as much as you can afford. You won't be sorry.

Bandwidth Is a Lot Like Plumbing

Plumbing provides a great analogy for bandwidth... seriously!

Data is to available bandwidth as water is to the size of the pipe.

In other words, as the bandwidth increases so does the amount of data that can flow through in a given amount of time, just like as the diameter of the pipe increases, so does the amount of water that can flow through during a period of time.

Say you're streaming a movie, someone else is playing an online multiplayer video game, and a couple others on your same network are downloading files or using their phones to watch online videos. It's likely that everyone will feel that things are a bit sluggish if not constantly starting and stopping. This has to do with bandwidth.

To return to the plumbing analogy, assuming the water pipe to a home (the bandwidth) remains the same size, as the home's faucets and showers are turned on (data downloads to the devices being used), the water pressure at each point (the perceived "speed" at each device) will reduce - again, because there's only so much water (bandwidth) available to the home (your network).

Put another way: the bandwidth is a fixed amount based on what you pay for, so, while one person may be able to stream a high-def video without any lag whatsoever, the moment you begin adding other download requests to the network, each one will get just their portion of the full capacity.

For example, if a speed test identifies my download speed as 7.85 Mbps, it means that given no interruptions or other bandwidth-hogging applications, I could download a 7.85 megabit (or 0.98 megabytes) file in one second.

A little math would tell you that at this allowed bandwidth, I could download about 60 MB of information in one minute, or 3,528 MB in an hour, which is equivalent to a 3.5 GB file... pretty close to a full-length, DVD-quality movie.

So while I could theoretically download a 3.5 GB video file in an hour, if someone else on my network tries to download a similar file at the same time, it would now take two hours to complete the download because again, the network only permits x amount of data to be downloaded at any given time, so it now must allow the other download to use some of that bandwidth too.

Technically, the network would now see 3.5 GB + 3.5 GB, for 7 GB of total data that needs downloaded. The bandwidth capacity doesn't change because that's a level you pay your ISP for, so the same concept applies - a 7.85 Mbps network is going to now take two hours to download the 7 GB file just like it would take just one hour to download half that amount.

The Difference in Mbps and MBps

It's important to understand that bandwidth can be expressed in any unit (bytes, kilobytes, megabytes, gigabits, etc.). Your ISP might use one term, a testing service another, and a video streaming service yet another. You'll need to understand how these terms are all related and how to convert between them if you want to avoid paying for too much internet service or, maybe worse, ordering too little for what you want to do with it.

For example, 15 MBs is not the same as 15 Mbs (note the lowercase b). The first reads as 15 megaBYTES while the second is 15 megaBITS. These two values are different by a factor of 8 since there are 8 bits in a byte.

If these two bandwidth readings were written in megabytes (MB), they'd be 15 MBs and 1.875 MBs (since 15/8 is 1.875). However, when written in megabits (Mb), the first would be 120 Mbs (15x8 is 120) and the second 15 Mbps.

Tip: This same concept applies to any data unit you might encounter. You can use an online conversion calculator like this one if you'd rather not do the math manually. See Terabytes, Gigabytes, & Petabytes: How Big are They? for more information.

More Information on Bandwidth

Some software lets you limit the amount of bandwidth that the program is allowed to use, which is really helpful if you still want the program to function but it doesn't necessarily need to be running at a certain speed. This intentional bandwidth limitation is often called bandwidth control.

Some download managers, like Free Download Manager, for example, support bandwidth control, as do numerous online backup services and some cloud storage services. These are all services and programs that tend to use massive amounts of bandwidth, so it makes sense to have options that limit their access.

As an example, say you want to download a really large 10 GB file. Instead of having it download for hours, sucking away all the available bandwidth, you could use a download manager and instruct the program to limit the download to use only 10% of the available bandwidth. This would of course drastically add time to the total download time but it would also free up a lot more bandwidth for other time-sensitive activities like live video streams.

Something similar to bandwidth control is bandwidth throttling. This is also a deliberate bandwidth control that's sometimes set by internet service providers to either limit certain types of traffic (like Netflix streaming or file sharing) or to limit all traffic during particular periods of time during the day in order to reduce congestion.

Network performance is determined by more than just how much bandwidth you have available. There are also factors like latency, jitter, and packet loss that could be contributing to less-than-desirable performance in any given network.