There is always a small difference between the memory capacity displayed on the package and the one displayed on a computer. There are two reasons for this:

I. Une Part of the memory of the memory card is reserved by the system for its own operation. This represents about 3% of the initial capacity of the USB stick.

Example:
A 32 GB memory card contains 32,000,000,000 bytes 32,000,000,000 - 3% = 31,000,000,000 = 31 GB after formatting the memory card

Depending on the type of formatting (file system) the difference will be more or less for the same memory card. See screenshots below*

II. Difference in the mode of calculation between human and computer :

The memory capacity of the memory cards is always indicated in the decimal system respecting the units of the International System (SI), this applies to the packaging, product sheets, and websites of the memory cards.
1 GB = 10⁹ bytes = 1 000 000 000 bytes = 1 billion bytes

However, computers do not work with the decimal system as humans do, but with the binary system. In the binary system the unit is the GiB and not the GB.
1 GiB = 2³⁰ bytes = 1 073 741 824 bytes

Example:
A 32 GB memory card with 31 GB free after formatting, or 31,000,000,000 bytes.
If we convert this value in GB: 31 000 000 000 / 1 000 000 000 = 31 GB
If we convert this value in GiB: 31 000 000 000 / 1 073 741 824 = 28.8 GiB
So 31 Gb = 28.8 Gb

III. To display the capacities of the memory card some OS (Operating System) display GB and others GiB.

Warning! Windows is an OS that does not respect the International System (IS).
In Windows the value of the memory capacities is displayed in binary (GiB) but the unit of capacity is displayed in Decimal (GB). This unit error can mislead the unsuspecting user because it generates a capacity difference of about 7%.

Windows rounds values to the tenth (one digit after the decimal point at most). Therefore: the values displayed in Windows should be 31 GB or 28.8 GiB but not 28.8 GB*.

Under MacOS the values and the unit of the memory capacities are in decimal. Apple respects the International System (SI).

The value displayed in MacOS is 31 GB*

IV. Value table

The values below are given as an indication and may vary depending on the memory card and the type of formatting

*All the screenshots on this page were taken with the same 32 GB USB key.