How Much Space Should Your External Drive Have?

Are you thinking about buying new external hard drive? If yes, then one of the following questions should be – How big storage do i need? 

Storage, nowadays, come in various forms from the traditional hard disk drive to the ubiquitous cloud storage. Typically, computers are equipped with an internal hard drive with about 500gb of disk space, some of which already consumed by the operating system and basic applications. Even when empty, the formatting of hard drives (NTFS, HFS, etc.) already take up quite a lot of space, typically around 35gb for a 500gb hard disk drive.

Basically you’re left with around 450 GB of hard disk space due to formatting overhead and operating system allocation. While this may not be a problem for casual computer users who only do light web surfing and word processing, people who download lossless music (FLAC, ALAC, etc.), high definition (HD) videos and images, games, and other types of data that consume a lot of space will find 450gb to be inadequate.

Also, computers can break down, taking your precious data along with it, which further emphasizes the need for secondary storage.

Fortunately, external hard disk drives provide a convenient way to store and transfer large files, whether as a means of backup, file transfer, or simply additional space. With that in mind, one is faced with the dilemma of choosing the capacity of the external hard disk drive. This guide aims to help you find the right size of external hard disk drive by taking you through the fundamentals of data sizes and other things you need to know to find the best external hard drive for your computer.

One Byte at a Time

When trying to determine how much space you need for your external hard drive, it’s important to know more about the basic units used for computer data, as well as the common data types and the space they typically consume. Think of this as figuring out the amount of space needed by each family member before purchasing a house; by knowing how much space each family member is going to be happy with, one gets to buy a house that gives everyone enough space to move around and grow.

The smallest unit of data is a bit (short for binary digit). A bit can contain only either 1 or 0. A byte has 8 bits, which means that it can store eight digits of 1’s and 0’s. Being able to store more 1’s and 0’s give computers more ways to represent data. Taking a step higher, we bump into the kilobyte (KB), which is basically a thousand bytes, as expressed by the kilo- prefix.

In most operating systems, however, one kilobyte actually contains 1024 bytes. While this may not be significant for USB flash drives and other forms of storage with less space, with larger external hard drives (especially those with more than 1TB of space), this difference may be overwhelming; since a lot of operating systems take one kilobyte as 1024 bytes, while hard drive manufacturers take one kilobyte as 1000 bytes, you’re basically left with less space than you’ve paid for – this is a huge factor you need to consider in choosing an external hard disk drive.

How Much Space You Really Need

If price wasn’t an issue, this guide would be completely useless, as one could just simply buy the external hard disk drive with the biggest capacity and be done with it. However, since people want the best value for their money, it becomes important to get only as much space as you can afford.

To date, external hard disk drives come in sizes that range from 300gb to a few terabytes. Currently the biggest dekstop external hard drive is Seagate Backup Plus with capacity up to 8TB. The capacity of the external hard disk drive you purchase will depend on the type and quantity of the files you need to store. The basic rule is that the more information it contains, the more space it eats up. This may not be too apparent, however, for multimedia files, especially with compression happening in the background.

The most obvious way to see this rule in action, however, is to create an empty text file and check out its file size. After taking note of its file size, copy and paste a huge chunk of text into it and see how the file size changes from about 0 or 1kb to a few hundreds or thousands. Try adding HD images to that text file and see how the file size jumps from a few kilobytes to a few megabytes.

Here’s a glance of common types of space-hungry data and how much space they typically consume:

  • Music – a typical mp3 file, on average, eats up about 5-7mb of space whereas a lossless audio file like FLAC could eat up 20-30mb of space.
  • Images – for compressed JPEG files, you’d typically expect around 700kb-2mb of space consumed. For PNG, Bitmap, and other files that experience minimal to no compression, however, you may be looking at 5mb onwards.
  • Video – a standard definition video (640×480) that’s about 30 seconds long can consume about 6mb of disk space. The same video in full 1080p HD, however, could get up to about 3.5gb! 

Based on the figures presented above, if you were to fill your 450gb hard drive up with multimedia content, you can put about 2 hours of full HD videos, about 90,000 PNG images, about 18,000 FLAC music, OR about 75,000 mp3 music. Everyday, however, there are always new podcasts, videos, songs, and other types of information available. A good formula to use in order to determine the right size of external hard disk drive is:

Space needed = [(Average number of music downloaded per day * Average size of music file type used) + (Average number of images downloaded per day * Average size of image file type used) + (Average number of videos downloaded per day * Average size of video file type used)] * [(5 years of expected usage before upgrade)*(365 days in a year)]

You may also add any other file type that you feel eats a significant amount of space. In any case, you should pick an external hard drive that has a bit more capacity than what the formula gives you in order to leave room for any unprecedented file additions (like an unforeseen emergency backup).

Don’t want to calculate storage capacity? 

A good hard disk drive space to start with is 1tb if you only plan on keeping mp3 files, a few 2-3mb pictures, and possibly a few HD videos that are at least compressed in the mkv format. If, however, you plan on keeping a classical music library (typically lossless), with a few PNG files and HD compressed videos, then go for 2tb. If you plan on keeping an HD movie library, uncompressed, raw image files, or quite a few FLAC music files, then go ahead and jump to the 4tb external hard drives.

Buying More to Save More

In supermarkets, one is often faced with the decision of buying in bulk to save money or buying in small increments to fit a fixed budgeting scheme. The same is true for hard disk drives; when you buy a larger capacity hard drive the price per byte is significantly smaller than if you buy a smaller capacity hard drive.

It makes sense when you think about it, as manufacturers only need to add a larger platter or more chips to add more space, but to manufacture another hard disk drive requires them to come up with a whole new set of parts. In a nutshell, it’s best to go for larger capacity hard disk drives when you have the money, as you actually save more in the long run.


External hard disk drives let you extend the available space on your computer without having to pry it open and risk damaging internal components. It also provides a way for you to easily migrate large files without having to rely on network connections. As you have seen in this guide, there is no such thing as the “perfect” external hard drive, as the perfect one would never run out of space, nor become obsolete in less than a decade.
That being said, it’s important for you to choose an external hard disk drive that contains just enough space for you to store your files until you decide to upgrade to a much larger external hard disk drive (the life span of hard disk drives is usually around 5 years, less when used heavily).

If you plan on storing only word and excel files, the minimum hard disk drive space should be enough (around 300gb). For multimedia content, a larger space is required (at least 1tb is a good start). Because hard drive manufacturers have a different way of measuring their capacity compared to software developers, make sure you leave room for discrepancy in terms of the defined capacity.

In any case, the rule of thumb is that bigger is always better, so opt for an external hard disk drive that has a balance of affordability and space. Do that, and you have yourself world of information tucked neatly for quite a long time.


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