Decimal and binary units

Decimal storage units use powers of 1,000: one kilobyte is 1,000 bytes and one gigabyte is 1,000,000,000 bytes. Binary IEC units use powers of 1,024: one kibibyte is 1,024 bytes and one gibibyte is 1,073,741,824 bytes.

Why displayed capacity differs

Storage manufacturers commonly state capacity in decimal units, while some operating systems display binary quantities using decimal-looking labels. A device sold as 1 TB contains one trillion bytes, equal to about 931.323 GiB before formatting and system use.

Bits are not bytes

A lowercase b normally means bit, while uppercase B means byte. Eight bits make one byte. Network speeds stated in megabits per second are therefore not directly equal to file sizes in megabytes.

Check a marketed-capacity example

A drive labeled 500 GB contains 500,000,000,000 bytes when the manufacturer uses decimal SI prefixes. Divide by 1,073,741,824 bytes per GiB to get about 465.66 GiB. Nothing vanished in that conversion: the same byte count is being grouped into larger binary units. Formatting, recovery partitions, over-provisioning, file-system metadata, snapshots, and installed files can reduce the capacity available to store new user data beyond this unit-label difference.

Plan from bytes, then add overhead

For backup or transfer planning, convert every source to bytes first, add the byte counts, and only then choose a display unit. Do not round each file or folder before summing. Add a separate allowance for growth, versions, compression uncertainty, redundancy, and temporary working space. SI prefixes such as kilo and giga represent powers of 1,000; the NIST SI prefix guide notes that binary powers require distinct prefixes such as kibi and gibi.

This tool converts byte-based quantities. Available device capacity can be lower because of formatting, reserved areas, redundancy, and system files.