How many photos can an average USB drive hold?

USB drives are not obsolete, despite what we sometimes hear (even from us). For some people, it’s an additional dedicated space outside of their phone or computer where they can store documents or photos without having to compete with their “Genshin Impact” installation. All these files are easy to access too: just plug the player into your device. Plus, even with inflated memory prices, they’re still quite affordable. You can reliably buy 64GB and 128GB sticks for $15 to $30, give or take – 256GB is where there’s an appreciable increase in price.

So how many photos can you store on a fairly inexpensive USB drive? Well, let’s take a 128 GB USB stick for example: if you transfer JPEG files directly captured with your smartphone at around 13 megapixels, you can store between 12,000 and 40,000 photos on this drive. If we had to choose an over-under, we would place it at approximately 24,000. This variation might surprise you, but it will make a little more sense if you consider the degree of generic image compression.

Even when controlling the resolution and formatting, you’ll find that photos tend to be sized very differently when comparing dark and bright scenes. Two rules of thumb come into play. The first is that image formats handle brightness data in ones and zeros and a lack of brightness in a given area will tend to generate a zero. Additionally, with JPEG, this format’s compression algorithm prioritizes preserving brightness in well-defined areas of contrast such as the edge of a sunlit object placed in front of a shadowed background. There are different compression priorities across formats such as HEIC, but the general goal remains the same, especially on the first rule.

By applying these rules to finer details and adding the complication of color data, it becomes difficult to determine a “typical” image size. Typical smartphone photos we take range from 3 to 6 MB, and we’ve seen some files reach 9 MB. That said, if we stick to 5 MB as the happy medium, we end up with an average figure of 23,800 photos on a 119 GB key. Wait a second: 119 GB?

You may also notice that your computer or phone is reporting less storage on your drive than advertised. Unfortunately, this is nothing new. Storage producers use base 10 or decimal data units to define and market their products, while computers, which perform binary calculations, use base 2 or binary units. This means that a gigabyte can be 1 billion bytes or 1,073,741,824 bytes, depending on your interpretation. Binary units have special industry-recognized names with binary prefixes that incorporate “bi” into the names of existing decimal orders of magnitude: instead of kilo, mega, and giga, you have kibi, mebi, and gibi.

Now, just because computers do their calculations in binary doesn’t mean they have to display binary units. There is actually little consistency between operating systems as to whether they display binary or decimal units. But the worst sin, in our opinion, occurs when those who choose to display binary units refer to them using decimal names. One such offender is Microsoft, and this is how you get a 128 GB disk reporting in Windows as having 119 GB (not gibibytes) of space.

To top it all off, any type of storage drive will loop a portion of their space that users cannot access. This partition contains dedicated firmware for the disk as well as infrastructure for storing and searching files, as well as recovery resources in the event of a disk failure, which you can take steps to avoid.