# What are the units of measurements for data storage?

The smallest unit of measurement for digital data is a bit. A single bit has two possible values — 0 and 1. When multiple bits are strung together, the number of possible values they can represent increases exponentially. For example, eight bits can store 256 possible values (2^{8}) and 10 bits can store 1,024 (2^{10}).

Data storage is measured in bytes, which are blocks of eight bits. A small file may only require a few bytes, while large files may contain millions or even billions of bytes. Storage devices can hold trillions of bytes, and server farms can store even greater amounts of data. Several units of measurement exist to represent these different levels of data storage.

### Decimal (SI) Units of Measurement

Kilobytes, megabytes, and gigabytes are units of digital storage with decimal prefixes, also known as SI prefixes. They represent round numbers of bytes in increasing orders of magnitude, as powers of 10. For example, a kilobyte is a thousand bytes (10^{3}), a megabyte is a million bytes (10^{6}), a gigabyte is a billion bytes (10^{9}), and so on.

Unit | Value | Size |
---|---|---|

bit (b) | 0 or 1 | 1/8 of a byte |

byte (B) | 8 bits | 1 byte |

kilobyte (KB) | 1000^{1} bytes |
1,000 bytes |

megabyte (MB) | 1000^{2} bytes |
1,000,000 bytes |

gigabyte (GB) | 1000^{3} bytes |
1,000,000,000 bytes |

terabyte (TB) | 1000^{4} bytes |
1,000,000,000,000 bytes |

petabyte (PB) | 1000^{5} bytes |
1,000,000,000,000,000 bytes |

exabyte (EB) | 1000^{6} bytes |
1,000,000,000,000,000,000 bytes |

zettabyte (ZB) | 1000^{7} bytes |
1,000,000,000,000,000,000,000 bytes |

yottabyte (YB) | 1000^{8} bytes |
1,000,000,000,000,000,000,000,000 bytes |

### Binary Units of Measurement

Kibibytes, mebibytes, gibibytes, and tebibytes, are units of digital storage that use binary prefixes and represent numbers of bytes as powers of 2. For example, a kibibyte is 1,024 bytes (2^{10}), a mebibyte is 1,048,576 bytes (2^{20}), and a gibibyte is 1,073,741,824 bytes (2^{30}).

Unit | Value | Size |
---|---|---|

bit (b) | 0 or 1 | 1/8 of a byte |

byte (B) | 8 bits | 1 byte |

kibibyte (KiB) | 2^{10} bytes |
1,024 bytes |

mebibyte (MiB) | 2^{20} (or 1,024^{2}) bytes |
1,048,576 bytes |

gibibyte (GiB) | 2^{30} (or 1,024^{3}) bytes |
1,073,741,824 bytes |

tebibyte (TiB) | 2^{40} (or 1,024^{4}) bytes |
1,099,511,627,776 bytes |

pebibyte (PiB) | 2^{50} (or 1,024^{5}) bytes |
1,125,899,906,842,624 bytes |

exbibyte (EiB) | 2^{60} (or 1,024^{6}) bytes |
1,152,921,504,606,846,976 bytes |

zebibyte (ZiB) | 2^{70} (or 1,024^{7}) bytes |
1,180,591,620,717,411,303,424 bytes |

yobibyte (YiB) | 2^{80} (or 1,024^{8}) bytes |
1,208,925,819,614,629,174,706,176 bytes |

### Binary vs Decimal Units of Measurement

Binary and decimal prefixes that start with the same letters are nearly equivalent, though binary units are slightly larger. For example, a kilobyte is 1,000 bytes and a kibibyte is 1,024 bytes — a difference of 24 bytes. As the units of measurement increases, the difference between the corresponding units increases as well.

Decimal value | Binary equivalent | Difference |
---|---|---|

100 kilobytes (KB) | 97.656 kibibytes (KiB) | 2.35% |

100 megabytes (MB) | 95.367 mebibytes (MiB) | 4.64% |

100 gigabytes (GB) | 93.132 gibibytes (GiB) | 6.87% |

100 terabytes (TB) | 90.95 tebibytes (TiB) | 9.05% |

100 petabytes (PB) | 88.818 pebibytes (PiB) | 11.18% |

100 exabytes (EB) | 86.736 exbibytes (EiB) | 13.26% |

100 zettabytes (ZB) | 84.703 zebibytes (ZiB) | 15.3% |

100 yottabytes (YB) | 82.718 yobibytes (YiB) | 17.28% |

**NOTE:** Hard drive sizes are often marketed with decimal units instead of binary units (for example, terabytes instead of tebibytes). Therefore, the capacity of a 1 TB hard drive may be slightly greater than 1 terabyte.