Why does my new storage device (USB Flash drive, SD memory card, SSD drive, etc) show less space than the package?

Many users are concerned that the capacity described on the packaging of their storage device is higher than what is shown to them by their operating system, like Microsoft Windows.  There are several reasons for this apparent discrepancy.

First, the standard for the terms that describe the KB, MB, GB, TB, etc capacity of a storage device is not the same standard for describing the capacity of a computer's main memory.  A gigabyte of storage (1,000,000,000 bytes) is not the same thing as what we often consider a gigabyte of memory (1,073,741,824 bytes).  In fact, the number "1,073,741,824" is actually officially a "gibibyte", not a "gigabyte".

Which leads to the second reason: operating systems display storage capacity using multiple standards and rarely correctly.  A 32GB storage device usually has at least 32 billion bytes (32,000,000,000) of unformatted capacity.  But the Properties window for such a device will show the capacity as 29.8GB instead of 32GB.  "29.8" is the number of gibibytes and should be abbreviated as "GiB".

Making things even more confusing, is that sometimes the calculation method changes within the same operating system.  Sometimes the operating system will show the capacity of this card in terms of megabytes, but incorrectly using a mebibyte (1,048,576) calculation.

The third reason is that the capacity usually shown to the user by the operating system is the capacity of the partition, not the entire physical storage.  The operating system uses some of the capacity of the storage device to create the partition and makes it unavailable to the user.

A final problem comes from losses incurred by the process of formatting and inefficiencies of storing data.  The capacity the user sees is an absolute capacity, but every file stored on a storage device uses more space that the actual file size because the file system is using part of the space to describe the location of the file on the storage device and because files use blocks of storage that are always larger than a single byte.

Below is a chart that shows what a user might expect to see with some common storage device capacities:

BytesMarked asShown by OS
512,000,000 512MB 488.3MB
1,000,000,000 1GB 953.7MB
2,000,000,000 2GB 1.9GB
4,000,000,000 4GB 3.7GB
8,000,000,000 8GB 7.5GB
16,000,000,000 16GB 14.9GB
32,000,000,000 32GB 29.8GB
64,000,000,000 64GB 59.6GB
128,000,000,000 128GB 119.2GB
256,000,000,000 256GB 238.4GB
512,000,000,000 512GB 476.8GB
1,000,000,000,000 1TB 931.3GB



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