Kilo (symbol: k) is a prefix in the SI system denoting 10³ or 1000. For example:

• kilogram is 1000 grams
• kilometre is 1000 metres
• kilowatt is 1000 watts
• kilojoule is 1000 joules

Adopted in 1795, it comes from the Greek χίλιοι, meaning thousand.

"Kilo" is often used by itself as an abbreviation for "kilogram". Also, technical people often use the term "k", pronounced like the letter, to refer to a thousand of something, especially units of money or population. The kilometre, on the other hand, is often abbreviated to "klick" in American, especially military usage.

Kilo is also the letter K in the NATO phonetic alphabet
Kilo class is a type of naval submarine made in Russia.

Use in computing

In computing, kilo does not always exactly denote 1000 but is usually equivalent to 1024 (2¹⁰), most often when denoting storage. For example, a kilobyte is 1024 bytes, not 1000 bytes. One prominent exception is the field of commodity hard drive manufacturing, where the smaller value is used in advertising and technical specifications. Additionally, kilo and mega often have their traditional SI meanings when referring to rates of data transfer. For instance, 56 kilobits per second is 56 000 bits per second, not 57 344 bits per second.

A common (but erroneous) convention is to use k for 1000 and K for 1024. The prefix kibi for "1024" has been introduced, but has not gained much popularity.