The Reason Why Your Drive Shows Less Storage Than You Paid For

Device storage is extremely valuable these days. The rabid appetite of AI datacenters is inflating drive pricing so badly that companies like Apple and Valve have jacked up the prices of some products by hundreds of dollars. Even if that wasn’t happening, though, the size of apps, media and operating systems is continually growing, filling up the storage we do have. Some PC and console games can top 100GB, especially if they’re live service titles with a lot of downloadable content.

All this is to say that if there’s a gap between the amount of storage you’re promised for an internal or external drive versus what’s actually usable, the disappointment may be palpable now more than ever. Recently, for example, we discovered that a 512GB drive only registered as offering 477GB accessible to Windows. On paper, that 35GB difference might be enough to fit someone’s entire photo library, or maybe a converted 4K HDR movie.

In most instances, the root of these discrepancies boils down to how different companies calculate data, rather than a naked attempt to rip you off. At other times, it may be a matter of a device being unusable without some of that space going to pre-installed software.

Frequently, storage makers calculate storage capacity using a base-10 (decimal) system. In that arrangement, a kilobyte is 1,000 bytes, a gigabyte is 1 billion bytes, and so forth. And that probably makes sense to you, given how measurements work in most other areas of life, especially if you live in a country using the metric system for weights and distances. It’s a lot easier to market to the average consumer.

The thing is, software platforms like Windows often gauge capacity in binary terms. That transforms a kilobyte into 1,024 bytes, and a gigabyte into 1,073,741,824 bytes. As figures get larger, the gap between binary and decimal calculations becomes vast. A 1TB drive may show as holding just 931GB in Windows, despite nothing actually being lost. You will see the full 1TB available on a Mac, where decimal reigns supreme.

This is obviously problematic if you’re expecting storage marketed in binary terms versus the way hardware makers label it. To our knowledge, Microsoft doesn’t have any intention of switching Windows from binary to decimal, and Apple isn’t planning to revert the Mac, iPad, iPhone or other products back to binary. You can expect this inconsistency to exist in the market for a while longer.

There have been attempts to make the situation clearer by using binary-specific terms such as “kibibyte” (KiB) and “gibibyte” (GiB). As you’ve probably noticed, though, these haven’t caught on, even within binary-based platforms. If you check the file size of something in Windows 11, you’ll see KB or GB instead. 

A complaint you’ll run into occasionally is that the new phone, tablet, laptop or console they bought doesn’t have as much usable space as they expected. This can potentially be linked to the binary-decimal split we just talked about, but the bigger culprit tends to be the device OS, which has to be pre-installed for anything to work. iOS 27 consumes over 22GB (decimal) on a 128GB iPhone 16 Pro, and on one of our gaming laptops, Windows 11 occupies over 81GB (binary). It’s no wonder that 64GB devices are effectively extinct, and that even 128GB is becoming impractical.

As if things weren’t complicated enough, operating systems tend to grow every year as new features are added. And to run smoothly, most devices need additional cache and swap space for temporary files. This space isn’t necessarily marked off-limits. If it isn’t, though, you can accidentally harm performance by downloading too many files or installing too many apps. Vanishing swap space bogs down performance, and can lead to apps crashing or freezing.

To cope with this unfortunate scenario, all you can really do is be conservative with your usage and shopping habits. If you avoid waste and overestimate the amount of storage you need, even a few dozen gigabytes can be an acceptable sacrifice. Don’t panic if you notice this when planning your next electronics haul.