Decimal storage units
In decimal storage, 1 kilobyte is 1,000 bytes, 1 megabyte is 1,000,000 bytes, and 1 gigabyte is 1,000,000,000 bytes. One terabyte is 1,000 gigabytes.
Hardware manufacturers and network services commonly use SI-based decimal prefixes. To convert MB to GB, divide by 1,000.
Binary units: KiB, MiB, and GiB
Binary units use powers of 1,024 and have distinct IEC names. One MiB is 1,048,576 bytes, and one GiB is 1,073,741,824 bytes.
Using KiB, MiB, and GiB removes ambiguity. A value labeled only KB, MB, or GB may be treated differently by different software.
Why a drive can appear smaller
A drive marketed as 1 TB contains 1,000,000,000,000 bytes. Reported with binary division, that is about 931.32 GiB.
The storage has not disappeared; the displayed number changes because the unit size changes. Formatting and file-system overhead can reduce usable capacity further.
Files, memory, and transfer estimates
Use decimal units when matching stated hardware capacity and binary units when software explicitly reports KiB, MiB, or GiB. Preserve the original label.
Storage size alone does not determine transfer time. Transfer calculations must distinguish bytes from bits and account for overhead and actual speed.