JUN 19, 2024

# File sizes explained: your guide to KB, MB, GB and more

Students of history might already know that original computer storage was on punch cards, with little holes in paper to represent the data that the era’s most powerful computers could understand.

We’ve come a long way since then, and computers are no longer just the province of scientific or military endeavors. Storage has come a long way since then too, but for a lot of us there’s not much understanding in how it all works, and why that matters when you’re buying a new phone, computer or even just an external storage device.

I mean, sometimes your phone plan says it has 20GB of downloads, or a phone says it has 128GB of storage, or an external hard drive says it has 2TB of storage. But what does that all actually mean when it comes to how much data a photo takes up? What about a music file? What if I’m streaming the latest hit show on my phone?

## Bits and Bytes

Unfortunately, in order to explain this all – and before I can explain to you the rough figures you can use to work out how much storage space you need or bandwidth your files will take up – we’ve got to do just a little bit of maths.

Don’t worry, most of it isn’t too hard to follow, and you don’t need to reach for a calculator. It’s important to know, however so that you can pick the differences between different storage measurements, and what they mean.

At the heart of any computing device, whether it’s a laptop, smartphone, gaming console or desktop computer, it’s only ever thinking in ones and zeroes. It’s a simplification, but one is “on” and zero is “off”, and that’s been the basis of what we call computers all the way back to those punch hole card computers that I mentioned earlier. They’re a bit faster than those models, mind you.

Those ones and zeroes are called “bits” in computing speak, and a bit is the fundamental unit of computing as it stands.

Gather together eight bits, and you’ve got yourself a byte. That group of eight bits is useful as it represents 256 different combinations across all of those on or off bits, so the computer can (effectively) count higher and do more complex calculations.

For typical storage these days you’ll never really see anything referred to in bits or bytes, but smaller files can measure in at the kilobyte range, or KB for short.

If you know your ancient Greek (or remember your maths) you might think that a kilobyte would be 1,000 bytes. It’s actually not, because of that binary system that computers use. 1,000 is a tricky number for a binary system to represent, but 1024 is more straightforward, mathematically speaking.

From kilobytes we jump to MB – Megabytes – which are 1024KB, then to GB – Gigabytes which are…

Yep, you got it, 1024 MB.

From GB you can step up to Terabytes (TB) which are 1024GB in a binary mathematical sense.

At a consumer level that’s where it largely stops, but if you’re talking really big data, 1024TB makes up a Petabyte (PT), and 1024PT makes up an Exabyte.

Trust me, you might think your photo library is big, but you don’t need an Exabyte scale drive, and you couldn’t afford one anyway.

## Hard drives think different

There’s a really important quirk to know about here if you’re buying an external hard drive, new laptop or desktop or phone. Most storage manufacturers will sell their devices with the storage measured in decimal – that’s base 10 – rather than binary scales.

So why does that matter? This is where the maths comes in handy, and I’ll use a 500GB drive as an example.

The label on the side that says 500GB isn’t lying, strictly speaking. However, plug that drive into your PC and it’ll show a capacity of around 465GB. Don’t panic. The other 35GB didn’t fall out of the side of the drive while you were getting it home.

The drive has 500GB if you measured each KB as 1,000 bytes. It’s 500 (the number of units) times 1,000 (Kilobytes) times 1,000 (Megabytes) times 1,000 (Gigabytes) for a total of 500,000,000,000 bytes if you measure them on that base 10 scale that we as humans use all the time.

Your computer, remember, thinks in binary, ones and twos, and to it, a Kilobyte is 1,024 bytes. Multiply 1024 out to the gigabyte scale, and your computer counts 1,073,741,824 bytes in a proper binary gigabyte. Divide that 500,000,000,000 (decimal gigabytes) by 1,073,741,824 and you get just over 465GB of data the way your computer sees it.

In reality, for a new computer or phone or tablet you’ll actually have less than this number anyway, because the operating system and its apps will take up some space too.

Before the panic sweats overtake you, no, you don’t need to remember a horrible number like 1,073,741,824 at all.

However, it’s worth keeping in mind when you’re backing up or copying data, because if you’ve got 500GB of files as your PC measures them, you’ll need a drive slightly larger than a 500GB advertised drive to stick them all onto.

## How much space do I need on my computer? What about for my phone plan?

With the tedious maths out of the way, you’ re probably champing at the bit to understand how much space a typical file takes up. It’s not a precise science, because different file types and compositions, and even the underlying software can make a big difference to how large a file is. The numbers below are really intended more to be “typical” file sizes and there’s room for them to be subtly different for different devices and services.

To give just one example of that, the smartphone you had ten years ago probably made photos that were around 1.5MB each, while a modern smartphone’s sensor typically takes photos somewhere between 3-4MB each, sometimes larger. If you’re using a DSLR to shoot in the RAW format, it’s way larger again. Higher quality music subscription services will stream files with less compression for smoother sound, at the cost of file sizes, and so on.

What does that mean in practical use? Here’s some typical figures, and how they’d measure up against that same 500GB hard drive, or a 20GB mobile broadband plan for a range of common file types.

For streaming video, a lot of services will let you dial quality down to save on file space; I’m using Netflix’s own “best” figures for data as an example here but as an example it does offer lower quality options for mobile devices through its app. Likewise for streaming audio, some mobile plans won’t “count” some music services if you’re streaming.

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